faceyspacey/react-universal-component

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Showing 42 of 42 total issues

Similar blocks of code found in 2 locations. Consider refactoring.
Open

    class Container extends React.Component {
      render() {
        const page = (this.state && this.state.page) || 'MyComponent'
        return <Component page={page} />
      }
Severity: Major
Found in __tests__/index.js and 1 other location - About 1 hr to fix
__tests__/index.js on lines 675..680

Duplicated Code

Duplicated code can lead to software that is hard to understand and difficult to change. The Don't Repeat Yourself (DRY) principle states:

Every piece of knowledge must have a single, unambiguous, authoritative representation within a system.

When you violate DRY, bugs and maintenance problems are sure to follow. Duplicated code has a tendency to both continue to replicate and also to diverge (leaving bugs as two similar implementations differ in subtle ways).

Tuning

This issue has a mass of 63.

We set useful threshold defaults for the languages we support but you may want to adjust these settings based on your project guidelines.

The threshold configuration represents the minimum mass a code block must have to be analyzed for duplication. The lower the threshold, the more fine-grained the comparison.

If the engine is too easily reporting duplication, try raising the threshold. If you suspect that the engine isn't catching enough duplication, try lowering the threshold. The best setting tends to differ from language to language.

See codeclimate-duplication's documentation for more information about tuning the mass threshold in your .codeclimate.yml.

Refactorings

Further Reading

Similar blocks of code found in 2 locations. Consider refactoring.
Open

    class Container extends React.Component {
      render() {
        const page = (this.state && this.state.page) || 'MyComponent'
        return <Component page={page} />
      }
Severity: Major
Found in __tests__/index.js and 1 other location - About 1 hr to fix
__tests__/index.js on lines 703..708

Duplicated Code

Duplicated code can lead to software that is hard to understand and difficult to change. The Don't Repeat Yourself (DRY) principle states:

Every piece of knowledge must have a single, unambiguous, authoritative representation within a system.

When you violate DRY, bugs and maintenance problems are sure to follow. Duplicated code has a tendency to both continue to replicate and also to diverge (leaving bugs as two similar implementations differ in subtle ways).

Tuning

This issue has a mass of 63.

We set useful threshold defaults for the languages we support but you may want to adjust these settings based on your project guidelines.

The threshold configuration represents the minimum mass a code block must have to be analyzed for duplication. The lower the threshold, the more fine-grained the comparison.

If the engine is too easily reporting duplication, try raising the threshold. If you suspect that the engine isn't catching enough duplication, try lowering the threshold. The best setting tends to differ from language to language.

See codeclimate-duplication's documentation for more information about tuning the mass threshold in your .codeclimate.yml.

Refactorings

Further Reading

Function componentDidUpdate has 28 lines of code (exceeds 25 allowed). Consider refactoring.
Open

    componentDidUpdate(prevProps: Props) {
      if (isDynamic || this._asyncOnly) {
        const { requireSync, requireAsync, shouldUpdate } = req(
          asyncModule,
          options,
Severity: Minor
Found in src/index.js - About 1 hr to fix

    Function requireAsync has 28 lines of code (exceeds 25 allowed). Consider refactoring.
    Open

      const requireAsync = (props: Object): Promise<?any> => {
        const exp = loadFromCache(chunkName, props, modCache)
        if (exp) return Promise.resolve(exp)
    
        const cachedPromise = loadFromPromiseCache(chunkName, props, promCache)
    Severity: Minor
    Found in src/requireUniversalModule.js - About 1 hr to fix

      Similar blocks of code found in 2 locations. Consider refactoring.
      Open

      export const flushChunkNames = (): Ids => {
        const chunks = Array.from(CHUNK_NAMES)
        CHUNK_NAMES.clear()
        return chunks
      }
      Severity: Minor
      Found in src/requireUniversalModule.js and 1 other location - About 40 mins to fix
      src/requireUniversalModule.js on lines 173..177

      Duplicated Code

      Duplicated code can lead to software that is hard to understand and difficult to change. The Don't Repeat Yourself (DRY) principle states:

      Every piece of knowledge must have a single, unambiguous, authoritative representation within a system.

      When you violate DRY, bugs and maintenance problems are sure to follow. Duplicated code has a tendency to both continue to replicate and also to diverge (leaving bugs as two similar implementations differ in subtle ways).

      Tuning

      This issue has a mass of 49.

      We set useful threshold defaults for the languages we support but you may want to adjust these settings based on your project guidelines.

      The threshold configuration represents the minimum mass a code block must have to be analyzed for duplication. The lower the threshold, the more fine-grained the comparison.

      If the engine is too easily reporting duplication, try raising the threshold. If you suspect that the engine isn't catching enough duplication, try lowering the threshold. The best setting tends to differ from language to language.

      See codeclimate-duplication's documentation for more information about tuning the mass threshold in your .codeclimate.yml.

      Refactorings

      Further Reading

      Similar blocks of code found in 2 locations. Consider refactoring.
      Open

      export const flushModuleIds = (): Ids => {
        const ids = Array.from(MODULE_IDS)
        MODULE_IDS.clear()
        return ids
      }
      Severity: Minor
      Found in src/requireUniversalModule.js and 1 other location - About 40 mins to fix
      src/requireUniversalModule.js on lines 167..171

      Duplicated Code

      Duplicated code can lead to software that is hard to understand and difficult to change. The Don't Repeat Yourself (DRY) principle states:

      Every piece of knowledge must have a single, unambiguous, authoritative representation within a system.

      When you violate DRY, bugs and maintenance problems are sure to follow. Duplicated code has a tendency to both continue to replicate and also to diverge (leaving bugs as two similar implementations differ in subtle ways).

      Tuning

      This issue has a mass of 49.

      We set useful threshold defaults for the languages we support but you may want to adjust these settings based on your project guidelines.

      The threshold configuration represents the minimum mass a code block must have to be analyzed for duplication. The lower the threshold, the more fine-grained the comparison.

      If the engine is too easily reporting duplication, try raising the threshold. If you suspect that the engine isn't catching enough duplication, try lowering the threshold. The best setting tends to differ from language to language.

      See codeclimate-duplication's documentation for more information about tuning the mass threshold in your .codeclimate.yml.

      Refactorings

      Further Reading

      Function getConfig has a Cognitive Complexity of 7 (exceeds 5 allowed). Consider refactoring.
      Open

      const getConfig = (
        isDynamic: ?boolean,
        universalConfig: Config | ConfigFunc,
        options: ModuleOptions,
        props: Props
      Severity: Minor
      Found in src/requireUniversalModule.js - About 35 mins to fix

      Cognitive Complexity

      Cognitive Complexity is a measure of how difficult a unit of code is to intuitively understand. Unlike Cyclomatic Complexity, which determines how difficult your code will be to test, Cognitive Complexity tells you how difficult your code will be to read and comprehend.

      A method's cognitive complexity is based on a few simple rules:

      • Code is not considered more complex when it uses shorthand that the language provides for collapsing multiple statements into one
      • Code is considered more complex for each "break in the linear flow of the code"
      • Code is considered more complex when "flow breaking structures are nested"

      Further reading

      Function __handleAfter has a Cognitive Complexity of 6 (exceeds 5 allowed). Consider refactoring.
      Open

      export const __handleAfter = (props, state, isMount, isSync, isServer) => {
        const { mod, error } = state
      
        if (mod && !error) {
          hoist(UniversalComponent, mod, {
      Severity: Minor
      Found in src/helpers.js - About 25 mins to fix

      Cognitive Complexity

      Cognitive Complexity is a measure of how difficult a unit of code is to intuitively understand. Unlike Cyclomatic Complexity, which determines how difficult your code will be to test, Cognitive Complexity tells you how difficult your code will be to read and comprehend.

      A method's cognitive complexity is based on a few simple rules:

      • Code is not considered more complex when it uses shorthand that the language provides for collapsing multiple statements into one
      • Code is considered more complex for each "break in the linear flow of the code"
      • Code is considered more complex when "flow breaking structures are nested"

      Further reading

      'cb' is defined but never used.
      Open

          const asyncComponent = async (props, cb) => {
      Severity: Minor
      Found in __tests__/index.js by eslint

      Disallow Unused Variables (no-unused-vars)

      Variables that are declared and not used anywhere in the code are most likely an error due to incomplete refactoring. Such variables take up space in the code and can lead to confusion by readers.

      Rule Details

      This rule is aimed at eliminating unused variables, functions, and parameters of functions.

      A variable is considered to be used if any of the following are true:

      • It represents a function that is called (doSomething())
      • It is read (var y = x)
      • It is passed into a function as an argument (doSomething(x))
      • It is read inside of a function that is passed to another function (doSomething(function() { foo(); }))

      A variable is not considered to be used if it is only ever assigned to (var x = 5) or declared.

      Examples of incorrect code for this rule:

      /*eslint no-unused-vars: "error"*/
      /*global some_unused_var*/
      
      // It checks variables you have defined as global
      some_unused_var = 42;
      
      var x;
      
      // Write-only variables are not considered as used.
      var y = 10;
      y = 5;
      
      // A read for a modification of itself is not considered as used.
      var z = 0;
      z = z + 1;
      
      // By default, unused arguments cause warnings.
      (function(foo) {
          return 5;
      })();
      
      // Unused recursive functions also cause warnings.
      function fact(n) {
          if (n < 2) return 1;
          return n * fact(n - 1);
      }
      
      // When a function definition destructures an array, unused entries from the array also cause warnings.
      function getY([x, y]) {
          return y;
      }

      Examples of correct code for this rule:

      /*eslint no-unused-vars: "error"*/
      
      var x = 10;
      alert(x);
      
      // foo is considered used here
      myFunc(function foo() {
          // ...
      }.bind(this));
      
      (function(foo) {
          return foo;
      })();
      
      var myFunc;
      myFunc = setTimeout(function() {
          // myFunc is considered used
          myFunc();
      }, 50);
      
      // Only the second argument from the descructured array is used.
      function getY([, y]) {
          return y;
      }

      exported

      In environments outside of CommonJS or ECMAScript modules, you may use var to create a global variable that may be used by other scripts. You can use the /* exported variableName */ comment block to indicate that this variable is being exported and therefore should not be considered unused.

      Note that /* exported */ has no effect for any of the following:

      • when the environment is node or commonjs
      • when parserOptions.sourceType is module
      • when ecmaFeatures.globalReturn is true

      The line comment // exported variableName will not work as exported is not line-specific.

      Examples of correct code for /* exported variableName */ operation:

      /* exported global_var */
      
      var global_var = 42;

      Options

      This rule takes one argument which can be a string or an object. The string settings are the same as those of the vars property (explained below).

      By default this rule is enabled with all option for variables and after-used for arguments.

      {
          "rules": {
              "no-unused-vars": ["error", { "vars": "all", "args": "after-used", "ignoreRestSiblings": false }]
          }
      }

      vars

      The vars option has two settings:

      • all checks all variables for usage, including those in the global scope. This is the default setting.
      • local checks only that locally-declared variables are used but will allow global variables to be unused.

      vars: local

      Examples of correct code for the { "vars": "local" } option:

      /*eslint no-unused-vars: ["error", { "vars": "local" }]*/
      /*global some_unused_var */
      
      some_unused_var = 42;

      varsIgnorePattern

      The varsIgnorePattern option specifies exceptions not to check for usage: variables whose names match a regexp pattern. For example, variables whose names contain ignored or Ignored.

      Examples of correct code for the { "varsIgnorePattern": "[iI]gnored" } option:

      /*eslint no-unused-vars: ["error", { "varsIgnorePattern": "[iI]gnored" }]*/
      
      var firstVarIgnored = 1;
      var secondVar = 2;
      console.log(secondVar);

      args

      The args option has three settings:

      • after-used - only the last argument must be used. This allows you, for instance, to have two named parameters to a function and as long as you use the second argument, ESLint will not warn you about the first. This is the default setting.
      • all - all named arguments must be used.
      • none - do not check arguments.

      args: after-used

      Examples of incorrect code for the default { "args": "after-used" } option:

      /*eslint no-unused-vars: ["error", { "args": "after-used" }]*/
      
      // 1 error
      // "baz" is defined but never used
      (function(foo, bar, baz) {
          return bar;
      })();

      Examples of correct code for the default { "args": "after-used" } option:

      /*eslint no-unused-vars: ["error", {"args": "after-used"}]*/
      
      (function(foo, bar, baz) {
          return baz;
      })();

      args: all

      Examples of incorrect code for the { "args": "all" } option:

      /*eslint no-unused-vars: ["error", { "args": "all" }]*/
      
      // 2 errors
      // "foo" is defined but never used
      // "baz" is defined but never used
      (function(foo, bar, baz) {
          return bar;
      })();

      args: none

      Examples of correct code for the { "args": "none" } option:

      /*eslint no-unused-vars: ["error", { "args": "none" }]*/
      
      (function(foo, bar, baz) {
          return bar;
      })();

      ignoreRestSiblings

      The ignoreRestSiblings option is a boolean (default: false). Using a Rest Property it is possible to "omit" properties from an object, but by default the sibling properties are marked as "unused". With this option enabled the rest property's siblings are ignored.

      Examples of correct code for the { "ignoreRestSiblings": true } option:

      /*eslint no-unused-vars: ["error", { "ignoreRestSiblings": true }]*/
      // 'type' is ignored because it has a rest property sibling.
      var { type, ...coords } = data;

      argsIgnorePattern

      The argsIgnorePattern option specifies exceptions not to check for usage: arguments whose names match a regexp pattern. For example, variables whose names begin with an underscore.

      Examples of correct code for the { "argsIgnorePattern": "^_" } option:

      /*eslint no-unused-vars: ["error", { "argsIgnorePattern": "^_" }]*/
      
      function foo(x, _y) {
          return x + 1;
      }
      foo();

      caughtErrors

      The caughtErrors option is used for catch block arguments validation.

      It has two settings:

      • none - do not check error objects. This is the default setting.
      • all - all named arguments must be used.

      caughtErrors: none

      Not specifying this rule is equivalent of assigning it to none.

      Examples of correct code for the { "caughtErrors": "none" } option:

      /*eslint no-unused-vars: ["error", { "caughtErrors": "none" }]*/
      
      try {
          //...
      } catch (err) {
          console.error("errors");
      }

      caughtErrors: all

      Examples of incorrect code for the { "caughtErrors": "all" } option:

      /*eslint no-unused-vars: ["error", { "caughtErrors": "all" }]*/
      
      // 1 error
      // "err" is defined but never used
      try {
          //...
      } catch (err) {
          console.error("errors");
      }

      caughtErrorsIgnorePattern

      The caughtErrorsIgnorePattern option specifies exceptions not to check for usage: catch arguments whose names match a regexp pattern. For example, variables whose names begin with a string 'ignore'.

      Examples of correct code for the { "caughtErrorsIgnorePattern": "^ignore" } option:

      /*eslint no-unused-vars: ["error", { "caughtErrorsIgnorePattern": "^ignore" }]*/
      
      try {
          //...
      } catch (ignoreErr) {
          console.error("errors");
      }

      When Not To Use It

      If you don't want to be notified about unused variables or function arguments, you can safely turn this rule off. Source: http://eslint.org/docs/rules/

      Expected to return a value at the end of method 'componentDidUpdate'.
      Open

          componentDidUpdate(prevProps: Props) {
      Severity: Minor
      Found in src/index.js by eslint

      require return statements to either always or never specify values (consistent-return)

      Unlike statically-typed languages which enforce that a function returns a specified type of value, JavaScript allows different code paths in a function to return different types of values.

      A confusing aspect of JavaScript is that a function returns undefined if any of the following are true:

      • it does not execute a return statement before it exits
      • it executes return which does not specify a value explicitly
      • it executes return undefined
      • it executes return void followed by an expression (for example, a function call)
      • it executes return followed by any other expression which evaluates to undefined

      If any code paths in a function return a value explicitly but some code path do not return a value explicitly, it might be a typing mistake, especially in a large function. In the following example:

      • a code path through the function returns a Boolean value true
      • another code path does not return a value explicitly, therefore returns undefined implicitly
      function doSomething(condition) {
          if (condition) {
              return true;
          } else {
              return;
          }
      }

      Rule Details

      This rule requires return statements to either always or never specify values. This rule ignores function definitions where the name begins with an uppercase letter, because constructors (when invoked with the new operator) return the instantiated object implicitly if they do not return another object explicitly.

      Examples of incorrect code for this rule:

      /*eslint consistent-return: "error"*/
      
      function doSomething(condition) {
          if (condition) {
              return true;
          } else {
              return;
          }
      }
      
      function doSomething(condition) {
          if (condition) {
              return true;
          }
      }

      Examples of correct code for this rule:

      /*eslint consistent-return: "error"*/
      
      function doSomething(condition) {
          if (condition) {
              return true;
          } else {
              return false;
          }
      }
      
      function Foo() {
          if (!(this instanceof Foo)) {
              return new Foo();
          }
      
          this.a = 0;
      }

      Options

      This rule has an object option:

      • "treatUndefinedAsUnspecified": false (default) always either specify values or return undefined implicitly only.
      • "treatUndefinedAsUnspecified": true always either specify values or return undefined explicitly or implicitly.

      treatUndefinedAsUnspecified

      Examples of incorrect code for this rule with the default { "treatUndefinedAsUnspecified": false } option:

      /*eslint consistent-return: ["error", { "treatUndefinedAsUnspecified": false }]*/
      
      function foo(callback) {
          if (callback) {
              return void callback();
          }
          // no return statement
      }
      
      function bar(condition) {
          if (condition) {
              return undefined;
          }
          // no return statement
      }

      Examples of incorrect code for this rule with the { "treatUndefinedAsUnspecified": true } option:

      /*eslint consistent-return: ["error", { "treatUndefinedAsUnspecified": true }]*/
      
      function foo(callback) {
          if (callback) {
              return void callback();
          }
          return true;
      }
      
      function bar(condition) {
          if (condition) {
              return undefined;
          }
          return true;
      }

      Examples of correct code for this rule with the { "treatUndefinedAsUnspecified": true } option:

      /*eslint consistent-return: ["error", { "treatUndefinedAsUnspecified": true }]*/
      
      function foo(callback) {
          if (callback) {
              return void callback();
          }
          // no return statement
      }
      
      function bar(condition) {
          if (condition) {
              return undefined;
          }
          // no return statement
      }

      When Not To Use It

      If you want to allow functions to have different return behavior depending on code branching, then it is safe to disable this rule. Source: http://eslint.org/docs/rules/

      Declare only one React component per file
      Open

          class Container extends React.Component {
      Severity: Minor
      Found in __tests__/index.js by eslint

      For more information visit Source: http://eslint.org/docs/rules/

      Method 'componentDidUpdate' expected a return value.
      Open

                  return
      Severity: Minor
      Found in src/index.js by eslint

      require return statements to either always or never specify values (consistent-return)

      Unlike statically-typed languages which enforce that a function returns a specified type of value, JavaScript allows different code paths in a function to return different types of values.

      A confusing aspect of JavaScript is that a function returns undefined if any of the following are true:

      • it does not execute a return statement before it exits
      • it executes return which does not specify a value explicitly
      • it executes return undefined
      • it executes return void followed by an expression (for example, a function call)
      • it executes return followed by any other expression which evaluates to undefined

      If any code paths in a function return a value explicitly but some code path do not return a value explicitly, it might be a typing mistake, especially in a large function. In the following example:

      • a code path through the function returns a Boolean value true
      • another code path does not return a value explicitly, therefore returns undefined implicitly
      function doSomething(condition) {
          if (condition) {
              return true;
          } else {
              return;
          }
      }

      Rule Details

      This rule requires return statements to either always or never specify values. This rule ignores function definitions where the name begins with an uppercase letter, because constructors (when invoked with the new operator) return the instantiated object implicitly if they do not return another object explicitly.

      Examples of incorrect code for this rule:

      /*eslint consistent-return: "error"*/
      
      function doSomething(condition) {
          if (condition) {
              return true;
          } else {
              return;
          }
      }
      
      function doSomething(condition) {
          if (condition) {
              return true;
          }
      }

      Examples of correct code for this rule:

      /*eslint consistent-return: "error"*/
      
      function doSomething(condition) {
          if (condition) {
              return true;
          } else {
              return false;
          }
      }
      
      function Foo() {
          if (!(this instanceof Foo)) {
              return new Foo();
          }
      
          this.a = 0;
      }

      Options

      This rule has an object option:

      • "treatUndefinedAsUnspecified": false (default) always either specify values or return undefined implicitly only.
      • "treatUndefinedAsUnspecified": true always either specify values or return undefined explicitly or implicitly.

      treatUndefinedAsUnspecified

      Examples of incorrect code for this rule with the default { "treatUndefinedAsUnspecified": false } option:

      /*eslint consistent-return: ["error", { "treatUndefinedAsUnspecified": false }]*/
      
      function foo(callback) {
          if (callback) {
              return void callback();
          }
          // no return statement
      }
      
      function bar(condition) {
          if (condition) {
              return undefined;
          }
          // no return statement
      }

      Examples of incorrect code for this rule with the { "treatUndefinedAsUnspecified": true } option:

      /*eslint consistent-return: ["error", { "treatUndefinedAsUnspecified": true }]*/
      
      function foo(callback) {
          if (callback) {
              return void callback();
          }
          return true;
      }
      
      function bar(condition) {
          if (condition) {
              return undefined;
          }
          return true;
      }

      Examples of correct code for this rule with the { "treatUndefinedAsUnspecified": true } option:

      /*eslint consistent-return: ["error", { "treatUndefinedAsUnspecified": true }]*/
      
      function foo(callback) {
          if (callback) {
              return void callback();
          }
          // no return statement
      }
      
      function bar(condition) {
          if (condition) {
              return undefined;
          }
          // no return statement
      }

      When Not To Use It

      If you want to allow functions to have different return behavior depending on code branching, then it is safe to disable this rule. Source: http://eslint.org/docs/rules/

      Expected to return a value at the end of arrow function.
      Open

            const resolve = mod => {
      Severity: Minor
      Found in src/requireUniversalModule.js by eslint

      require return statements to either always or never specify values (consistent-return)

      Unlike statically-typed languages which enforce that a function returns a specified type of value, JavaScript allows different code paths in a function to return different types of values.

      A confusing aspect of JavaScript is that a function returns undefined if any of the following are true:

      • it does not execute a return statement before it exits
      • it executes return which does not specify a value explicitly
      • it executes return undefined
      • it executes return void followed by an expression (for example, a function call)
      • it executes return followed by any other expression which evaluates to undefined

      If any code paths in a function return a value explicitly but some code path do not return a value explicitly, it might be a typing mistake, especially in a large function. In the following example:

      • a code path through the function returns a Boolean value true
      • another code path does not return a value explicitly, therefore returns undefined implicitly
      function doSomething(condition) {
          if (condition) {
              return true;
          } else {
              return;
          }
      }

      Rule Details

      This rule requires return statements to either always or never specify values. This rule ignores function definitions where the name begins with an uppercase letter, because constructors (when invoked with the new operator) return the instantiated object implicitly if they do not return another object explicitly.

      Examples of incorrect code for this rule:

      /*eslint consistent-return: "error"*/
      
      function doSomething(condition) {
          if (condition) {
              return true;
          } else {
              return;
          }
      }
      
      function doSomething(condition) {
          if (condition) {
              return true;
          }
      }

      Examples of correct code for this rule:

      /*eslint consistent-return: "error"*/
      
      function doSomething(condition) {
          if (condition) {
              return true;
          } else {
              return false;
          }
      }
      
      function Foo() {
          if (!(this instanceof Foo)) {
              return new Foo();
          }
      
          this.a = 0;
      }

      Options

      This rule has an object option:

      • "treatUndefinedAsUnspecified": false (default) always either specify values or return undefined implicitly only.
      • "treatUndefinedAsUnspecified": true always either specify values or return undefined explicitly or implicitly.

      treatUndefinedAsUnspecified

      Examples of incorrect code for this rule with the default { "treatUndefinedAsUnspecified": false } option:

      /*eslint consistent-return: ["error", { "treatUndefinedAsUnspecified": false }]*/
      
      function foo(callback) {
          if (callback) {
              return void callback();
          }
          // no return statement
      }
      
      function bar(condition) {
          if (condition) {
              return undefined;
          }
          // no return statement
      }

      Examples of incorrect code for this rule with the { "treatUndefinedAsUnspecified": true } option:

      /*eslint consistent-return: ["error", { "treatUndefinedAsUnspecified": true }]*/
      
      function foo(callback) {
          if (callback) {
              return void callback();
          }
          return true;
      }
      
      function bar(condition) {
          if (condition) {
              return undefined;
          }
          return true;
      }

      Examples of correct code for this rule with the { "treatUndefinedAsUnspecified": true } option:

      /*eslint consistent-return: ["error", { "treatUndefinedAsUnspecified": true }]*/
      
      function foo(callback) {
          if (callback) {
              return void callback();
          }
          // no return statement
      }
      
      function bar(condition) {
          if (condition) {
              return undefined;
          }
          // no return statement
      }

      When Not To Use It

      If you want to allow functions to have different return behavior depending on code branching, then it is safe to disable this rule. Source: http://eslint.org/docs/rules/

      Expected to return a value at the end of arrow function.
      Open

        const addModule = (props: Object): ?string => {
      Severity: Minor
      Found in src/requireUniversalModule.js by eslint

      require return statements to either always or never specify values (consistent-return)

      Unlike statically-typed languages which enforce that a function returns a specified type of value, JavaScript allows different code paths in a function to return different types of values.

      A confusing aspect of JavaScript is that a function returns undefined if any of the following are true:

      • it does not execute a return statement before it exits
      • it executes return which does not specify a value explicitly
      • it executes return undefined
      • it executes return void followed by an expression (for example, a function call)
      • it executes return followed by any other expression which evaluates to undefined

      If any code paths in a function return a value explicitly but some code path do not return a value explicitly, it might be a typing mistake, especially in a large function. In the following example:

      • a code path through the function returns a Boolean value true
      • another code path does not return a value explicitly, therefore returns undefined implicitly
      function doSomething(condition) {
          if (condition) {
              return true;
          } else {
              return;
          }
      }

      Rule Details

      This rule requires return statements to either always or never specify values. This rule ignores function definitions where the name begins with an uppercase letter, because constructors (when invoked with the new operator) return the instantiated object implicitly if they do not return another object explicitly.

      Examples of incorrect code for this rule:

      /*eslint consistent-return: "error"*/
      
      function doSomething(condition) {
          if (condition) {
              return true;
          } else {
              return;
          }
      }
      
      function doSomething(condition) {
          if (condition) {
              return true;
          }
      }

      Examples of correct code for this rule:

      /*eslint consistent-return: "error"*/
      
      function doSomething(condition) {
          if (condition) {
              return true;
          } else {
              return false;
          }
      }
      
      function Foo() {
          if (!(this instanceof Foo)) {
              return new Foo();
          }
      
          this.a = 0;
      }

      Options

      This rule has an object option:

      • "treatUndefinedAsUnspecified": false (default) always either specify values or return undefined implicitly only.
      • "treatUndefinedAsUnspecified": true always either specify values or return undefined explicitly or implicitly.

      treatUndefinedAsUnspecified

      Examples of incorrect code for this rule with the default { "treatUndefinedAsUnspecified": false } option:

      /*eslint consistent-return: ["error", { "treatUndefinedAsUnspecified": false }]*/
      
      function foo(callback) {
          if (callback) {
              return void callback();
          }
          // no return statement
      }
      
      function bar(condition) {
          if (condition) {
              return undefined;
          }
          // no return statement
      }

      Examples of incorrect code for this rule with the { "treatUndefinedAsUnspecified": true } option:

      /*eslint consistent-return: ["error", { "treatUndefinedAsUnspecified": true }]*/
      
      function foo(callback) {
          if (callback) {
              return void callback();
          }
          return true;
      }
      
      function bar(condition) {
          if (condition) {
              return undefined;
          }
          return true;
      }

      Examples of correct code for this rule with the { "treatUndefinedAsUnspecified": true } option:

      /*eslint consistent-return: ["error", { "treatUndefinedAsUnspecified": true }]*/
      
      function foo(callback) {
          if (callback) {
              return void callback();
          }
          // no return statement
      }
      
      function bar(condition) {
          if (condition) {
              return undefined;
          }
          // no return statement
      }

      When Not To Use It

      If you want to allow functions to have different return behavior depending on code branching, then it is safe to disable this rule. Source: http://eslint.org/docs/rules/

      'isWebpack' is defined but never used.
      Open

      export const createDynamicBablePluginApp = isWebpack => {
      Severity: Minor
      Found in __test-helpers__/createApp.js by eslint

      Disallow Unused Variables (no-unused-vars)

      Variables that are declared and not used anywhere in the code are most likely an error due to incomplete refactoring. Such variables take up space in the code and can lead to confusion by readers.

      Rule Details

      This rule is aimed at eliminating unused variables, functions, and parameters of functions.

      A variable is considered to be used if any of the following are true:

      • It represents a function that is called (doSomething())
      • It is read (var y = x)
      • It is passed into a function as an argument (doSomething(x))
      • It is read inside of a function that is passed to another function (doSomething(function() { foo(); }))

      A variable is not considered to be used if it is only ever assigned to (var x = 5) or declared.

      Examples of incorrect code for this rule:

      /*eslint no-unused-vars: "error"*/
      /*global some_unused_var*/
      
      // It checks variables you have defined as global
      some_unused_var = 42;
      
      var x;
      
      // Write-only variables are not considered as used.
      var y = 10;
      y = 5;
      
      // A read for a modification of itself is not considered as used.
      var z = 0;
      z = z + 1;
      
      // By default, unused arguments cause warnings.
      (function(foo) {
          return 5;
      })();
      
      // Unused recursive functions also cause warnings.
      function fact(n) {
          if (n < 2) return 1;
          return n * fact(n - 1);
      }
      
      // When a function definition destructures an array, unused entries from the array also cause warnings.
      function getY([x, y]) {
          return y;
      }

      Examples of correct code for this rule:

      /*eslint no-unused-vars: "error"*/
      
      var x = 10;
      alert(x);
      
      // foo is considered used here
      myFunc(function foo() {
          // ...
      }.bind(this));
      
      (function(foo) {
          return foo;
      })();
      
      var myFunc;
      myFunc = setTimeout(function() {
          // myFunc is considered used
          myFunc();
      }, 50);
      
      // Only the second argument from the descructured array is used.
      function getY([, y]) {
          return y;
      }

      exported

      In environments outside of CommonJS or ECMAScript modules, you may use var to create a global variable that may be used by other scripts. You can use the /* exported variableName */ comment block to indicate that this variable is being exported and therefore should not be considered unused.

      Note that /* exported */ has no effect for any of the following:

      • when the environment is node or commonjs
      • when parserOptions.sourceType is module
      • when ecmaFeatures.globalReturn is true

      The line comment // exported variableName will not work as exported is not line-specific.

      Examples of correct code for /* exported variableName */ operation:

      /* exported global_var */
      
      var global_var = 42;

      Options

      This rule takes one argument which can be a string or an object. The string settings are the same as those of the vars property (explained below).

      By default this rule is enabled with all option for variables and after-used for arguments.

      {
          "rules": {
              "no-unused-vars": ["error", { "vars": "all", "args": "after-used", "ignoreRestSiblings": false }]
          }
      }

      vars

      The vars option has two settings:

      • all checks all variables for usage, including those in the global scope. This is the default setting.
      • local checks only that locally-declared variables are used but will allow global variables to be unused.

      vars: local

      Examples of correct code for the { "vars": "local" } option:

      /*eslint no-unused-vars: ["error", { "vars": "local" }]*/
      /*global some_unused_var */
      
      some_unused_var = 42;

      varsIgnorePattern

      The varsIgnorePattern option specifies exceptions not to check for usage: variables whose names match a regexp pattern. For example, variables whose names contain ignored or Ignored.

      Examples of correct code for the { "varsIgnorePattern": "[iI]gnored" } option:

      /*eslint no-unused-vars: ["error", { "varsIgnorePattern": "[iI]gnored" }]*/
      
      var firstVarIgnored = 1;
      var secondVar = 2;
      console.log(secondVar);

      args

      The args option has three settings:

      • after-used - only the last argument must be used. This allows you, for instance, to have two named parameters to a function and as long as you use the second argument, ESLint will not warn you about the first. This is the default setting.
      • all - all named arguments must be used.
      • none - do not check arguments.

      args: after-used

      Examples of incorrect code for the default { "args": "after-used" } option:

      /*eslint no-unused-vars: ["error", { "args": "after-used" }]*/
      
      // 1 error
      // "baz" is defined but never used
      (function(foo, bar, baz) {
          return bar;
      })();

      Examples of correct code for the default { "args": "after-used" } option:

      /*eslint no-unused-vars: ["error", {"args": "after-used"}]*/
      
      (function(foo, bar, baz) {
          return baz;
      })();

      args: all

      Examples of incorrect code for the { "args": "all" } option:

      /*eslint no-unused-vars: ["error", { "args": "all" }]*/
      
      // 2 errors
      // "foo" is defined but never used
      // "baz" is defined but never used
      (function(foo, bar, baz) {
          return bar;
      })();

      args: none

      Examples of correct code for the { "args": "none" } option:

      /*eslint no-unused-vars: ["error", { "args": "none" }]*/
      
      (function(foo, bar, baz) {
          return bar;
      })();

      ignoreRestSiblings

      The ignoreRestSiblings option is a boolean (default: false). Using a Rest Property it is possible to "omit" properties from an object, but by default the sibling properties are marked as "unused". With this option enabled the rest property's siblings are ignored.

      Examples of correct code for the { "ignoreRestSiblings": true } option:

      /*eslint no-unused-vars: ["error", { "ignoreRestSiblings": true }]*/
      // 'type' is ignored because it has a rest property sibling.
      var { type, ...coords } = data;

      argsIgnorePattern

      The argsIgnorePattern option specifies exceptions not to check for usage: arguments whose names match a regexp pattern. For example, variables whose names begin with an underscore.

      Examples of correct code for the { "argsIgnorePattern": "^_" } option:

      /*eslint no-unused-vars: ["error", { "argsIgnorePattern": "^_" }]*/
      
      function foo(x, _y) {
          return x + 1;
      }
      foo();

      caughtErrors

      The caughtErrors option is used for catch block arguments validation.

      It has two settings:

      • none - do not check error objects. This is the default setting.
      • all - all named arguments must be used.

      caughtErrors: none

      Not specifying this rule is equivalent of assigning it to none.

      Examples of correct code for the { "caughtErrors": "none" } option:

      /*eslint no-unused-vars: ["error", { "caughtErrors": "none" }]*/
      
      try {
          //...
      } catch (err) {
          console.error("errors");
      }

      caughtErrors: all

      Examples of incorrect code for the { "caughtErrors": "all" } option:

      /*eslint no-unused-vars: ["error", { "caughtErrors": "all" }]*/
      
      // 1 error
      // "err" is defined but never used
      try {
          //...
      } catch (err) {
          console.error("errors");
      }

      caughtErrorsIgnorePattern

      The caughtErrorsIgnorePattern option specifies exceptions not to check for usage: catch arguments whose names match a regexp pattern. For example, variables whose names begin with a string 'ignore'.

      Examples of correct code for the { "caughtErrorsIgnorePattern": "^ignore" } option:

      /*eslint no-unused-vars: ["error", { "caughtErrorsIgnorePattern": "^ignore" }]*/
      
      try {
          //...
      } catch (ignoreErr) {
          console.error("errors");
      }

      When Not To Use It

      If you don't want to be notified about unused variables or function arguments, you can safely turn this rule off. Source: http://eslint.org/docs/rules/

      'PropTypes' is defined but never used.
      Open

      import PropTypes from 'prop-types'
      Severity: Minor
      Found in src/index.js by eslint

      Disallow Unused Variables (no-unused-vars)

      Variables that are declared and not used anywhere in the code are most likely an error due to incomplete refactoring. Such variables take up space in the code and can lead to confusion by readers.

      Rule Details

      This rule is aimed at eliminating unused variables, functions, and parameters of functions.

      A variable is considered to be used if any of the following are true:

      • It represents a function that is called (doSomething())
      • It is read (var y = x)
      • It is passed into a function as an argument (doSomething(x))
      • It is read inside of a function that is passed to another function (doSomething(function() { foo(); }))

      A variable is not considered to be used if it is only ever assigned to (var x = 5) or declared.

      Examples of incorrect code for this rule:

      /*eslint no-unused-vars: "error"*/
      /*global some_unused_var*/
      
      // It checks variables you have defined as global
      some_unused_var = 42;
      
      var x;
      
      // Write-only variables are not considered as used.
      var y = 10;
      y = 5;
      
      // A read for a modification of itself is not considered as used.
      var z = 0;
      z = z + 1;
      
      // By default, unused arguments cause warnings.
      (function(foo) {
          return 5;
      })();
      
      // Unused recursive functions also cause warnings.
      function fact(n) {
          if (n < 2) return 1;
          return n * fact(n - 1);
      }
      
      // When a function definition destructures an array, unused entries from the array also cause warnings.
      function getY([x, y]) {
          return y;
      }

      Examples of correct code for this rule:

      /*eslint no-unused-vars: "error"*/
      
      var x = 10;
      alert(x);
      
      // foo is considered used here
      myFunc(function foo() {
          // ...
      }.bind(this));
      
      (function(foo) {
          return foo;
      })();
      
      var myFunc;
      myFunc = setTimeout(function() {
          // myFunc is considered used
          myFunc();
      }, 50);
      
      // Only the second argument from the descructured array is used.
      function getY([, y]) {
          return y;
      }

      exported

      In environments outside of CommonJS or ECMAScript modules, you may use var to create a global variable that may be used by other scripts. You can use the /* exported variableName */ comment block to indicate that this variable is being exported and therefore should not be considered unused.

      Note that /* exported */ has no effect for any of the following:

      • when the environment is node or commonjs
      • when parserOptions.sourceType is module
      • when ecmaFeatures.globalReturn is true

      The line comment // exported variableName will not work as exported is not line-specific.

      Examples of correct code for /* exported variableName */ operation:

      /* exported global_var */
      
      var global_var = 42;

      Options

      This rule takes one argument which can be a string or an object. The string settings are the same as those of the vars property (explained below).

      By default this rule is enabled with all option for variables and after-used for arguments.

      {
          "rules": {
              "no-unused-vars": ["error", { "vars": "all", "args": "after-used", "ignoreRestSiblings": false }]
          }
      }

      vars

      The vars option has two settings:

      • all checks all variables for usage, including those in the global scope. This is the default setting.
      • local checks only that locally-declared variables are used but will allow global variables to be unused.

      vars: local

      Examples of correct code for the { "vars": "local" } option:

      /*eslint no-unused-vars: ["error", { "vars": "local" }]*/
      /*global some_unused_var */
      
      some_unused_var = 42;

      varsIgnorePattern

      The varsIgnorePattern option specifies exceptions not to check for usage: variables whose names match a regexp pattern. For example, variables whose names contain ignored or Ignored.

      Examples of correct code for the { "varsIgnorePattern": "[iI]gnored" } option:

      /*eslint no-unused-vars: ["error", { "varsIgnorePattern": "[iI]gnored" }]*/
      
      var firstVarIgnored = 1;
      var secondVar = 2;
      console.log(secondVar);

      args

      The args option has three settings:

      • after-used - only the last argument must be used. This allows you, for instance, to have two named parameters to a function and as long as you use the second argument, ESLint will not warn you about the first. This is the default setting.
      • all - all named arguments must be used.
      • none - do not check arguments.

      args: after-used

      Examples of incorrect code for the default { "args": "after-used" } option:

      /*eslint no-unused-vars: ["error", { "args": "after-used" }]*/
      
      // 1 error
      // "baz" is defined but never used
      (function(foo, bar, baz) {
          return bar;
      })();

      Examples of correct code for the default { "args": "after-used" } option:

      /*eslint no-unused-vars: ["error", {"args": "after-used"}]*/
      
      (function(foo, bar, baz) {
          return baz;
      })();

      args: all

      Examples of incorrect code for the { "args": "all" } option:

      /*eslint no-unused-vars: ["error", { "args": "all" }]*/
      
      // 2 errors
      // "foo" is defined but never used
      // "baz" is defined but never used
      (function(foo, bar, baz) {
          return bar;
      })();

      args: none

      Examples of correct code for the { "args": "none" } option:

      /*eslint no-unused-vars: ["error", { "args": "none" }]*/
      
      (function(foo, bar, baz) {
          return bar;
      })();

      ignoreRestSiblings

      The ignoreRestSiblings option is a boolean (default: false). Using a Rest Property it is possible to "omit" properties from an object, but by default the sibling properties are marked as "unused". With this option enabled the rest property's siblings are ignored.

      Examples of correct code for the { "ignoreRestSiblings": true } option:

      /*eslint no-unused-vars: ["error", { "ignoreRestSiblings": true }]*/
      // 'type' is ignored because it has a rest property sibling.
      var { type, ...coords } = data;

      argsIgnorePattern

      The argsIgnorePattern option specifies exceptions not to check for usage: arguments whose names match a regexp pattern. For example, variables whose names begin with an underscore.

      Examples of correct code for the { "argsIgnorePattern": "^_" } option:

      /*eslint no-unused-vars: ["error", { "argsIgnorePattern": "^_" }]*/
      
      function foo(x, _y) {
          return x + 1;
      }
      foo();

      caughtErrors

      The caughtErrors option is used for catch block arguments validation.

      It has two settings:

      • none - do not check error objects. This is the default setting.
      • all - all named arguments must be used.

      caughtErrors: none

      Not specifying this rule is equivalent of assigning it to none.

      Examples of correct code for the { "caughtErrors": "none" } option:

      /*eslint no-unused-vars: ["error", { "caughtErrors": "none" }]*/
      
      try {
          //...
      } catch (err) {
          console.error("errors");
      }

      caughtErrors: all

      Examples of incorrect code for the { "caughtErrors": "all" } option:

      /*eslint no-unused-vars: ["error", { "caughtErrors": "all" }]*/
      
      // 1 error
      // "err" is defined but never used
      try {
          //...
      } catch (err) {
          console.error("errors");
      }

      caughtErrorsIgnorePattern

      The caughtErrorsIgnorePattern option specifies exceptions not to check for usage: catch arguments whose names match a regexp pattern. For example, variables whose names begin with a string 'ignore'.

      Examples of correct code for the { "caughtErrorsIgnorePattern": "^ignore" } option:

      /*eslint no-unused-vars: ["error", { "caughtErrorsIgnorePattern": "^ignore" }]*/
      
      try {
          //...
      } catch (ignoreErr) {
          console.error("errors");
      }

      When Not To Use It

      If you don't want to be notified about unused variables or function arguments, you can safely turn this rule off. Source: http://eslint.org/docs/rules/

      'prevProps' is defined but never used.
      Open

        prevProps?: Props
      Severity: Minor
      Found in src/requireUniversalModule.js by eslint

      Disallow Unused Variables (no-unused-vars)

      Variables that are declared and not used anywhere in the code are most likely an error due to incomplete refactoring. Such variables take up space in the code and can lead to confusion by readers.

      Rule Details

      This rule is aimed at eliminating unused variables, functions, and parameters of functions.

      A variable is considered to be used if any of the following are true:

      • It represents a function that is called (doSomething())
      • It is read (var y = x)
      • It is passed into a function as an argument (doSomething(x))
      • It is read inside of a function that is passed to another function (doSomething(function() { foo(); }))

      A variable is not considered to be used if it is only ever assigned to (var x = 5) or declared.

      Examples of incorrect code for this rule:

      /*eslint no-unused-vars: "error"*/
      /*global some_unused_var*/
      
      // It checks variables you have defined as global
      some_unused_var = 42;
      
      var x;
      
      // Write-only variables are not considered as used.
      var y = 10;
      y = 5;
      
      // A read for a modification of itself is not considered as used.
      var z = 0;
      z = z + 1;
      
      // By default, unused arguments cause warnings.
      (function(foo) {
          return 5;
      })();
      
      // Unused recursive functions also cause warnings.
      function fact(n) {
          if (n < 2) return 1;
          return n * fact(n - 1);
      }
      
      // When a function definition destructures an array, unused entries from the array also cause warnings.
      function getY([x, y]) {
          return y;
      }

      Examples of correct code for this rule:

      /*eslint no-unused-vars: "error"*/
      
      var x = 10;
      alert(x);
      
      // foo is considered used here
      myFunc(function foo() {
          // ...
      }.bind(this));
      
      (function(foo) {
          return foo;
      })();
      
      var myFunc;
      myFunc = setTimeout(function() {
          // myFunc is considered used
          myFunc();
      }, 50);
      
      // Only the second argument from the descructured array is used.
      function getY([, y]) {
          return y;
      }

      exported

      In environments outside of CommonJS or ECMAScript modules, you may use var to create a global variable that may be used by other scripts. You can use the /* exported variableName */ comment block to indicate that this variable is being exported and therefore should not be considered unused.

      Note that /* exported */ has no effect for any of the following:

      • when the environment is node or commonjs
      • when parserOptions.sourceType is module
      • when ecmaFeatures.globalReturn is true

      The line comment // exported variableName will not work as exported is not line-specific.

      Examples of correct code for /* exported variableName */ operation:

      /* exported global_var */
      
      var global_var = 42;

      Options

      This rule takes one argument which can be a string or an object. The string settings are the same as those of the vars property (explained below).

      By default this rule is enabled with all option for variables and after-used for arguments.

      {
          "rules": {
              "no-unused-vars": ["error", { "vars": "all", "args": "after-used", "ignoreRestSiblings": false }]
          }
      }

      vars

      The vars option has two settings:

      • all checks all variables for usage, including those in the global scope. This is the default setting.
      • local checks only that locally-declared variables are used but will allow global variables to be unused.

      vars: local

      Examples of correct code for the { "vars": "local" } option:

      /*eslint no-unused-vars: ["error", { "vars": "local" }]*/
      /*global some_unused_var */
      
      some_unused_var = 42;

      varsIgnorePattern

      The varsIgnorePattern option specifies exceptions not to check for usage: variables whose names match a regexp pattern. For example, variables whose names contain ignored or Ignored.

      Examples of correct code for the { "varsIgnorePattern": "[iI]gnored" } option:

      /*eslint no-unused-vars: ["error", { "varsIgnorePattern": "[iI]gnored" }]*/
      
      var firstVarIgnored = 1;
      var secondVar = 2;
      console.log(secondVar);

      args

      The args option has three settings:

      • after-used - only the last argument must be used. This allows you, for instance, to have two named parameters to a function and as long as you use the second argument, ESLint will not warn you about the first. This is the default setting.
      • all - all named arguments must be used.
      • none - do not check arguments.

      args: after-used

      Examples of incorrect code for the default { "args": "after-used" } option:

      /*eslint no-unused-vars: ["error", { "args": "after-used" }]*/
      
      // 1 error
      // "baz" is defined but never used
      (function(foo, bar, baz) {
          return bar;
      })();

      Examples of correct code for the default { "args": "after-used" } option:

      /*eslint no-unused-vars: ["error", {"args": "after-used"}]*/
      
      (function(foo, bar, baz) {
          return baz;
      })();

      args: all

      Examples of incorrect code for the { "args": "all" } option:

      /*eslint no-unused-vars: ["error", { "args": "all" }]*/
      
      // 2 errors
      // "foo" is defined but never used
      // "baz" is defined but never used
      (function(foo, bar, baz) {
          return bar;
      })();

      args: none

      Examples of correct code for the { "args": "none" } option:

      /*eslint no-unused-vars: ["error", { "args": "none" }]*/
      
      (function(foo, bar, baz) {
          return bar;
      })();

      ignoreRestSiblings

      The ignoreRestSiblings option is a boolean (default: false). Using a Rest Property it is possible to "omit" properties from an object, but by default the sibling properties are marked as "unused". With this option enabled the rest property's siblings are ignored.

      Examples of correct code for the { "ignoreRestSiblings": true } option:

      /*eslint no-unused-vars: ["error", { "ignoreRestSiblings": true }]*/
      // 'type' is ignored because it has a rest property sibling.
      var { type, ...coords } = data;

      argsIgnorePattern

      The argsIgnorePattern option specifies exceptions not to check for usage: arguments whose names match a regexp pattern. For example, variables whose names begin with an underscore.

      Examples of correct code for the { "argsIgnorePattern": "^_" } option:

      /*eslint no-unused-vars: ["error", { "argsIgnorePattern": "^_" }]*/
      
      function foo(x, _y) {
          return x + 1;
      }
      foo();

      caughtErrors

      The caughtErrors option is used for catch block arguments validation.

      It has two settings:

      • none - do not check error objects. This is the default setting.
      • all - all named arguments must be used.

      caughtErrors: none

      Not specifying this rule is equivalent of assigning it to none.

      Examples of correct code for the { "caughtErrors": "none" } option:

      /*eslint no-unused-vars: ["error", { "caughtErrors": "none" }]*/
      
      try {
          //...
      } catch (err) {
          console.error("errors");
      }

      caughtErrors: all

      Examples of incorrect code for the { "caughtErrors": "all" } option:

      /*eslint no-unused-vars: ["error", { "caughtErrors": "all" }]*/
      
      // 1 error
      // "err" is defined but never used
      try {
          //...
      } catch (err) {
          console.error("errors");
      }

      caughtErrorsIgnorePattern

      The caughtErrorsIgnorePattern option specifies exceptions not to check for usage: catch arguments whose names match a regexp pattern. For example, variables whose names begin with a string 'ignore'.

      Examples of correct code for the { "caughtErrorsIgnorePattern": "^ignore" } option:

      /*eslint no-unused-vars: ["error", { "caughtErrorsIgnorePattern": "^ignore" }]*/
      
      try {
          //...
      } catch (ignoreErr) {
          console.error("errors");
      }

      When Not To Use It

      If you don't want to be notified about unused variables or function arguments, you can safely turn this rule off. Source: http://eslint.org/docs/rules/

      'Props' is defined but never used.
      Open

        Props,
      Severity: Minor
      Found in src/index.js by eslint

      Disallow Unused Variables (no-unused-vars)

      Variables that are declared and not used anywhere in the code are most likely an error due to incomplete refactoring. Such variables take up space in the code and can lead to confusion by readers.

      Rule Details

      This rule is aimed at eliminating unused variables, functions, and parameters of functions.

      A variable is considered to be used if any of the following are true:

      • It represents a function that is called (doSomething())
      • It is read (var y = x)
      • It is passed into a function as an argument (doSomething(x))
      • It is read inside of a function that is passed to another function (doSomething(function() { foo(); }))

      A variable is not considered to be used if it is only ever assigned to (var x = 5) or declared.

      Examples of incorrect code for this rule:

      /*eslint no-unused-vars: "error"*/
      /*global some_unused_var*/
      
      // It checks variables you have defined as global
      some_unused_var = 42;
      
      var x;
      
      // Write-only variables are not considered as used.
      var y = 10;
      y = 5;
      
      // A read for a modification of itself is not considered as used.
      var z = 0;
      z = z + 1;
      
      // By default, unused arguments cause warnings.
      (function(foo) {
          return 5;
      })();
      
      // Unused recursive functions also cause warnings.
      function fact(n) {
          if (n < 2) return 1;
          return n * fact(n - 1);
      }
      
      // When a function definition destructures an array, unused entries from the array also cause warnings.
      function getY([x, y]) {
          return y;
      }

      Examples of correct code for this rule:

      /*eslint no-unused-vars: "error"*/
      
      var x = 10;
      alert(x);
      
      // foo is considered used here
      myFunc(function foo() {
          // ...
      }.bind(this));
      
      (function(foo) {
          return foo;
      })();
      
      var myFunc;
      myFunc = setTimeout(function() {
          // myFunc is considered used
          myFunc();
      }, 50);
      
      // Only the second argument from the descructured array is used.
      function getY([, y]) {
          return y;
      }

      exported

      In environments outside of CommonJS or ECMAScript modules, you may use var to create a global variable that may be used by other scripts. You can use the /* exported variableName */ comment block to indicate that this variable is being exported and therefore should not be considered unused.

      Note that /* exported */ has no effect for any of the following:

      • when the environment is node or commonjs
      • when parserOptions.sourceType is module
      • when ecmaFeatures.globalReturn is true

      The line comment // exported variableName will not work as exported is not line-specific.

      Examples of correct code for /* exported variableName */ operation:

      /* exported global_var */
      
      var global_var = 42;

      Options

      This rule takes one argument which can be a string or an object. The string settings are the same as those of the vars property (explained below).

      By default this rule is enabled with all option for variables and after-used for arguments.

      {
          "rules": {
              "no-unused-vars": ["error", { "vars": "all", "args": "after-used", "ignoreRestSiblings": false }]
          }
      }

      vars

      The vars option has two settings:

      • all checks all variables for usage, including those in the global scope. This is the default setting.
      • local checks only that locally-declared variables are used but will allow global variables to be unused.

      vars: local

      Examples of correct code for the { "vars": "local" } option:

      /*eslint no-unused-vars: ["error", { "vars": "local" }]*/
      /*global some_unused_var */
      
      some_unused_var = 42;

      varsIgnorePattern

      The varsIgnorePattern option specifies exceptions not to check for usage: variables whose names match a regexp pattern. For example, variables whose names contain ignored or Ignored.

      Examples of correct code for the { "varsIgnorePattern": "[iI]gnored" } option:

      /*eslint no-unused-vars: ["error", { "varsIgnorePattern": "[iI]gnored" }]*/
      
      var firstVarIgnored = 1;
      var secondVar = 2;
      console.log(secondVar);

      args

      The args option has three settings:

      • after-used - only the last argument must be used. This allows you, for instance, to have two named parameters to a function and as long as you use the second argument, ESLint will not warn you about the first. This is the default setting.
      • all - all named arguments must be used.
      • none - do not check arguments.

      args: after-used

      Examples of incorrect code for the default { "args": "after-used" } option:

      /*eslint no-unused-vars: ["error", { "args": "after-used" }]*/
      
      // 1 error
      // "baz" is defined but never used
      (function(foo, bar, baz) {
          return bar;
      })();

      Examples of correct code for the default { "args": "after-used" } option:

      /*eslint no-unused-vars: ["error", {"args": "after-used"}]*/
      
      (function(foo, bar, baz) {
          return baz;
      })();

      args: all

      Examples of incorrect code for the { "args": "all" } option:

      /*eslint no-unused-vars: ["error", { "args": "all" }]*/
      
      // 2 errors
      // "foo" is defined but never used
      // "baz" is defined but never used
      (function(foo, bar, baz) {
          return bar;
      })();

      args: none

      Examples of correct code for the { "args": "none" } option:

      /*eslint no-unused-vars: ["error", { "args": "none" }]*/
      
      (function(foo, bar, baz) {
          return bar;
      })();

      ignoreRestSiblings

      The ignoreRestSiblings option is a boolean (default: false). Using a Rest Property it is possible to "omit" properties from an object, but by default the sibling properties are marked as "unused". With this option enabled the rest property's siblings are ignored.

      Examples of correct code for the { "ignoreRestSiblings": true } option:

      /*eslint no-unused-vars: ["error", { "ignoreRestSiblings": true }]*/
      // 'type' is ignored because it has a rest property sibling.
      var { type, ...coords } = data;

      argsIgnorePattern

      The argsIgnorePattern option specifies exceptions not to check for usage: arguments whose names match a regexp pattern. For example, variables whose names begin with an underscore.

      Examples of correct code for the { "argsIgnorePattern": "^_" } option:

      /*eslint no-unused-vars: ["error", { "argsIgnorePattern": "^_" }]*/
      
      function foo(x, _y) {
          return x + 1;
      }
      foo();

      caughtErrors

      The caughtErrors option is used for catch block arguments validation.

      It has two settings:

      • none - do not check error objects. This is the default setting.
      • all - all named arguments must be used.

      caughtErrors: none

      Not specifying this rule is equivalent of assigning it to none.

      Examples of correct code for the { "caughtErrors": "none" } option:

      /*eslint no-unused-vars: ["error", { "caughtErrors": "none" }]*/
      
      try {
          //...
      } catch (err) {
          console.error("errors");
      }

      caughtErrors: all

      Examples of incorrect code for the { "caughtErrors": "all" } option:

      /*eslint no-unused-vars: ["error", { "caughtErrors": "all" }]*/
      
      // 1 error
      // "err" is defined but never used
      try {
          //...
      } catch (err) {
          console.error("errors");
      }

      caughtErrorsIgnorePattern

      The caughtErrorsIgnorePattern option specifies exceptions not to check for usage: catch arguments whose names match a regexp pattern. For example, variables whose names begin with a string 'ignore'.

      Examples of correct code for the { "caughtErrorsIgnorePattern": "^ignore" } option:

      /*eslint no-unused-vars: ["error", { "caughtErrorsIgnorePattern": "^ignore" }]*/
      
      try {
          //...
      } catch (ignoreErr) {
          console.error("errors");
      }

      When Not To Use It

      If you don't want to be notified about unused variables or function arguments, you can safely turn this rule off. Source: http://eslint.org/docs/rules/

      'name' is defined but never used.
      Open

        const create = name => {
      Severity: Minor
      Found in __test-helpers__/createApp.js by eslint

      Disallow Unused Variables (no-unused-vars)

      Variables that are declared and not used anywhere in the code are most likely an error due to incomplete refactoring. Such variables take up space in the code and can lead to confusion by readers.

      Rule Details

      This rule is aimed at eliminating unused variables, functions, and parameters of functions.

      A variable is considered to be used if any of the following are true:

      • It represents a function that is called (doSomething())
      • It is read (var y = x)
      • It is passed into a function as an argument (doSomething(x))
      • It is read inside of a function that is passed to another function (doSomething(function() { foo(); }))

      A variable is not considered to be used if it is only ever assigned to (var x = 5) or declared.

      Examples of incorrect code for this rule:

      /*eslint no-unused-vars: "error"*/
      /*global some_unused_var*/
      
      // It checks variables you have defined as global
      some_unused_var = 42;
      
      var x;
      
      // Write-only variables are not considered as used.
      var y = 10;
      y = 5;
      
      // A read for a modification of itself is not considered as used.
      var z = 0;
      z = z + 1;
      
      // By default, unused arguments cause warnings.
      (function(foo) {
          return 5;
      })();
      
      // Unused recursive functions also cause warnings.
      function fact(n) {
          if (n < 2) return 1;
          return n * fact(n - 1);
      }
      
      // When a function definition destructures an array, unused entries from the array also cause warnings.
      function getY([x, y]) {
          return y;
      }

      Examples of correct code for this rule:

      /*eslint no-unused-vars: "error"*/
      
      var x = 10;
      alert(x);
      
      // foo is considered used here
      myFunc(function foo() {
          // ...
      }.bind(this));
      
      (function(foo) {
          return foo;
      })();
      
      var myFunc;
      myFunc = setTimeout(function() {
          // myFunc is considered used
          myFunc();
      }, 50);
      
      // Only the second argument from the descructured array is used.
      function getY([, y]) {
          return y;
      }

      exported

      In environments outside of CommonJS or ECMAScript modules, you may use var to create a global variable that may be used by other scripts. You can use the /* exported variableName */ comment block to indicate that this variable is being exported and therefore should not be considered unused.

      Note that /* exported */ has no effect for any of the following:

      • when the environment is node or commonjs
      • when parserOptions.sourceType is module
      • when ecmaFeatures.globalReturn is true

      The line comment // exported variableName will not work as exported is not line-specific.

      Examples of correct code for /* exported variableName */ operation:

      /* exported global_var */
      
      var global_var = 42;

      Options

      This rule takes one argument which can be a string or an object. The string settings are the same as those of the vars property (explained below).

      By default this rule is enabled with all option for variables and after-used for arguments.

      {
          "rules": {
              "no-unused-vars": ["error", { "vars": "all", "args": "after-used", "ignoreRestSiblings": false }]
          }
      }

      vars

      The vars option has two settings:

      • all checks all variables for usage, including those in the global scope. This is the default setting.
      • local checks only that locally-declared variables are used but will allow global variables to be unused.

      vars: local

      Examples of correct code for the { "vars": "local" } option:

      /*eslint no-unused-vars: ["error", { "vars": "local" }]*/
      /*global some_unused_var */
      
      some_unused_var = 42;

      varsIgnorePattern

      The varsIgnorePattern option specifies exceptions not to check for usage: variables whose names match a regexp pattern. For example, variables whose names contain ignored or Ignored.

      Examples of correct code for the { "varsIgnorePattern": "[iI]gnored" } option:

      /*eslint no-unused-vars: ["error", { "varsIgnorePattern": "[iI]gnored" }]*/
      
      var firstVarIgnored = 1;
      var secondVar = 2;
      console.log(secondVar);

      args

      The args option has three settings:

      • after-used - only the last argument must be used. This allows you, for instance, to have two named parameters to a function and as long as you use the second argument, ESLint will not warn you about the first. This is the default setting.
      • all - all named arguments must be used.
      • none - do not check arguments.

      args: after-used

      Examples of incorrect code for the default { "args": "after-used" } option:

      /*eslint no-unused-vars: ["error", { "args": "after-used" }]*/
      
      // 1 error
      // "baz" is defined but never used
      (function(foo, bar, baz) {
          return bar;
      })();

      Examples of correct code for the default { "args": "after-used" } option:

      /*eslint no-unused-vars: ["error", {"args": "after-used"}]*/
      
      (function(foo, bar, baz) {
          return baz;
      })();

      args: all

      Examples of incorrect code for the { "args": "all" } option:

      /*eslint no-unused-vars: ["error", { "args": "all" }]*/
      
      // 2 errors
      // "foo" is defined but never used
      // "baz" is defined but never used
      (function(foo, bar, baz) {
          return bar;
      })();

      args: none

      Examples of correct code for the { "args": "none" } option:

      /*eslint no-unused-vars: ["error", { "args": "none" }]*/
      
      (function(foo, bar, baz) {
          return bar;
      })();

      ignoreRestSiblings

      The ignoreRestSiblings option is a boolean (default: false). Using a Rest Property it is possible to "omit" properties from an object, but by default the sibling properties are marked as "unused". With this option enabled the rest property's siblings are ignored.

      Examples of correct code for the { "ignoreRestSiblings": true } option:

      /*eslint no-unused-vars: ["error", { "ignoreRestSiblings": true }]*/
      // 'type' is ignored because it has a rest property sibling.
      var { type, ...coords } = data;

      argsIgnorePattern

      The argsIgnorePattern option specifies exceptions not to check for usage: arguments whose names match a regexp pattern. For example, variables whose names begin with an underscore.

      Examples of correct code for the { "argsIgnorePattern": "^_" } option:

      /*eslint no-unused-vars: ["error", { "argsIgnorePattern": "^_" }]*/
      
      function foo(x, _y) {
          return x + 1;
      }
      foo();

      caughtErrors

      The caughtErrors option is used for catch block arguments validation.

      It has two settings:

      • none - do not check error objects. This is the default setting.
      • all - all named arguments must be used.

      caughtErrors: none

      Not specifying this rule is equivalent of assigning it to none.

      Examples of correct code for the { "caughtErrors": "none" } option:

      /*eslint no-unused-vars: ["error", { "caughtErrors": "none" }]*/
      
      try {
          //...
      } catch (err) {
          console.error("errors");
      }

      caughtErrors: all

      Examples of incorrect code for the { "caughtErrors": "all" } option:

      /*eslint no-unused-vars: ["error", { "caughtErrors": "all" }]*/
      
      // 1 error
      // "err" is defined but never used
      try {
          //...
      } catch (err) {
          console.error("errors");
      }

      caughtErrorsIgnorePattern

      The caughtErrorsIgnorePattern option specifies exceptions not to check for usage: catch arguments whose names match a regexp pattern. For example, variables whose names begin with a string 'ignore'.

      Examples of correct code for the { "caughtErrorsIgnorePattern": "^ignore" } option:

      /*eslint no-unused-vars: ["error", { "caughtErrorsIgnorePattern": "^ignore" }]*/
      
      try {
          //...
      } catch (ignoreErr) {
          console.error("errors");
      }

      When Not To Use It

      If you don't want to be notified about unused variables or function arguments, you can safely turn this rule off. Source: http://eslint.org/docs/rules/

      'isWebpack' is defined but never used.
      Open

      export const createBablePluginApp = isWebpack => {
      Severity: Minor
      Found in __test-helpers__/createApp.js by eslint

      Disallow Unused Variables (no-unused-vars)

      Variables that are declared and not used anywhere in the code are most likely an error due to incomplete refactoring. Such variables take up space in the code and can lead to confusion by readers.

      Rule Details

      This rule is aimed at eliminating unused variables, functions, and parameters of functions.

      A variable is considered to be used if any of the following are true:

      • It represents a function that is called (doSomething())
      • It is read (var y = x)
      • It is passed into a function as an argument (doSomething(x))
      • It is read inside of a function that is passed to another function (doSomething(function() { foo(); }))

      A variable is not considered to be used if it is only ever assigned to (var x = 5) or declared.

      Examples of incorrect code for this rule:

      /*eslint no-unused-vars: "error"*/
      /*global some_unused_var*/
      
      // It checks variables you have defined as global
      some_unused_var = 42;
      
      var x;
      
      // Write-only variables are not considered as used.
      var y = 10;
      y = 5;
      
      // A read for a modification of itself is not considered as used.
      var z = 0;
      z = z + 1;
      
      // By default, unused arguments cause warnings.
      (function(foo) {
          return 5;
      })();
      
      // Unused recursive functions also cause warnings.
      function fact(n) {
          if (n < 2) return 1;
          return n * fact(n - 1);
      }
      
      // When a function definition destructures an array, unused entries from the array also cause warnings.
      function getY([x, y]) {
          return y;
      }

      Examples of correct code for this rule:

      /*eslint no-unused-vars: "error"*/
      
      var x = 10;
      alert(x);
      
      // foo is considered used here
      myFunc(function foo() {
          // ...
      }.bind(this));
      
      (function(foo) {
          return foo;
      })();
      
      var myFunc;
      myFunc = setTimeout(function() {
          // myFunc is considered used
          myFunc();
      }, 50);
      
      // Only the second argument from the descructured array is used.
      function getY([, y]) {
          return y;
      }

      exported

      In environments outside of CommonJS or ECMAScript modules, you may use var to create a global variable that may be used by other scripts. You can use the /* exported variableName */ comment block to indicate that this variable is being exported and therefore should not be considered unused.

      Note that /* exported */ has no effect for any of the following:

      • when the environment is node or commonjs
      • when parserOptions.sourceType is module
      • when ecmaFeatures.globalReturn is true

      The line comment // exported variableName will not work as exported is not line-specific.

      Examples of correct code for /* exported variableName */ operation:

      /* exported global_var */
      
      var global_var = 42;

      Options

      This rule takes one argument which can be a string or an object. The string settings are the same as those of the vars property (explained below).

      By default this rule is enabled with all option for variables and after-used for arguments.

      {
          "rules": {
              "no-unused-vars": ["error", { "vars": "all", "args": "after-used", "ignoreRestSiblings": false }]
          }
      }

      vars

      The vars option has two settings:

      • all checks all variables for usage, including those in the global scope. This is the default setting.
      • local checks only that locally-declared variables are used but will allow global variables to be unused.

      vars: local

      Examples of correct code for the { "vars": "local" } option:

      /*eslint no-unused-vars: ["error", { "vars": "local" }]*/
      /*global some_unused_var */
      
      some_unused_var = 42;

      varsIgnorePattern

      The varsIgnorePattern option specifies exceptions not to check for usage: variables whose names match a regexp pattern. For example, variables whose names contain ignored or Ignored.

      Examples of correct code for the { "varsIgnorePattern": "[iI]gnored" } option:

      /*eslint no-unused-vars: ["error", { "varsIgnorePattern": "[iI]gnored" }]*/
      
      var firstVarIgnored = 1;
      var secondVar = 2;
      console.log(secondVar);

      args

      The args option has three settings:

      • after-used - only the last argument must be used. This allows you, for instance, to have two named parameters to a function and as long as you use the second argument, ESLint will not warn you about the first. This is the default setting.
      • all - all named arguments must be used.
      • none - do not check arguments.

      args: after-used

      Examples of incorrect code for the default { "args": "after-used" } option:

      /*eslint no-unused-vars: ["error", { "args": "after-used" }]*/
      
      // 1 error
      // "baz" is defined but never used
      (function(foo, bar, baz) {
          return bar;
      })();

      Examples of correct code for the default { "args": "after-used" } option:

      /*eslint no-unused-vars: ["error", {"args": "after-used"}]*/
      
      (function(foo, bar, baz) {
          return baz;
      })();

      args: all

      Examples of incorrect code for the { "args": "all" } option:

      /*eslint no-unused-vars: ["error", { "args": "all" }]*/
      
      // 2 errors
      // "foo" is defined but never used
      // "baz" is defined but never used
      (function(foo, bar, baz) {
          return bar;
      })();

      args: none

      Examples of correct code for the { "args": "none" } option:

      /*eslint no-unused-vars: ["error", { "args": "none" }]*/
      
      (function(foo, bar, baz) {
          return bar;
      })();

      ignoreRestSiblings

      The ignoreRestSiblings option is a boolean (default: false). Using a Rest Property it is possible to "omit" properties from an object, but by default the sibling properties are marked as "unused". With this option enabled the rest property's siblings are ignored.

      Examples of correct code for the { "ignoreRestSiblings": true } option:

      /*eslint no-unused-vars: ["error", { "ignoreRestSiblings": true }]*/
      // 'type' is ignored because it has a rest property sibling.
      var { type, ...coords } = data;

      argsIgnorePattern

      The argsIgnorePattern option specifies exceptions not to check for usage: arguments whose names match a regexp pattern. For example, variables whose names begin with an underscore.

      Examples of correct code for the { "argsIgnorePattern": "^_" } option:

      /*eslint no-unused-vars: ["error", { "argsIgnorePattern": "^_" }]*/
      
      function foo(x, _y) {
          return x + 1;
      }
      foo();

      caughtErrors

      The caughtErrors option is used for catch block arguments validation.

      It has two settings:

      • none - do not check error objects. This is the default setting.
      • all - all named arguments must be used.

      caughtErrors: none

      Not specifying this rule is equivalent of assigning it to none.

      Examples of correct code for the { "caughtErrors": "none" } option:

      /*eslint no-unused-vars: ["error", { "caughtErrors": "none" }]*/
      
      try {
          //...
      } catch (err) {
          console.error("errors");
      }

      caughtErrors: all

      Examples of incorrect code for the { "caughtErrors": "all" } option:

      /*eslint no-unused-vars: ["error", { "caughtErrors": "all" }]*/
      
      // 1 error
      // "err" is defined but never used
      try {
          //...
      } catch (err) {
          console.error("errors");
      }

      caughtErrorsIgnorePattern

      The caughtErrorsIgnorePattern option specifies exceptions not to check for usage: catch arguments whose names match a regexp pattern. For example, variables whose names begin with a string 'ignore'.

      Examples of correct code for the { "caughtErrorsIgnorePattern": "^ignore" } option:

      /*eslint no-unused-vars: ["error", { "caughtErrorsIgnorePattern": "^ignore" }]*/
      
      try {
          //...
      } catch (ignoreErr) {
          console.error("errors");
      }

      When Not To Use It

      If you don't want to be notified about unused variables or function arguments, you can safely turn this rule off. Source: http://eslint.org/docs/rules/

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