Showing 437 of 437 total issues
Freeze mutable objects assigned to constants. Open
ATTRIBUTE_TYPES = {
users: Field::HasMany,
id: Field::Number,
created_at: Field::DateTime,
updated_at: Field::DateTime,
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- Exclude checks
This cop checks whether some constant value isn't a mutable literal (e.g. array or hash).
Example:
# bad
CONST = [1, 2, 3]
# good
CONST = [1, 2, 3].freeze
Line is too long. [82/80] Open
# Setup all fixtures in test/fixtures/*.yml for all tests in alphabetical order.
- Exclude checks
Indent the right brace the same as the first position after the preceding left parenthesis. Open
})['results']
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- Exclude checks
This cops checks the indentation of the first key in a hash literal where the opening brace and the first key are on separate lines. The other keys' indentations are handled by the AlignHash cop.
By default, Hash literals that are arguments in a method call with parentheses, and where the opening curly brace of the hash is on the same line as the opening parenthesis of the method call, shall have their first key indented one step (two spaces) more than the position inside the opening parenthesis.
Other hash literals shall have their first key indented one step more than the start of the line where the opening curly brace is.
This default style is called 'specialinsideparentheses'. Alternative styles are 'consistent' and 'align_braces'. Here are examples:
Example: EnforcedStyle: specialinsideparentheses (default)
# The `special_inside_parentheses` style enforces that the first key
# in a hash literal where the opening brace and the first key are on
# separate lines is indented one step (two spaces) more than the
# position inside the opening parentheses.
# bad
hash = {
key: :value
}
and_in_a_method_call({
no: :difference
})
# good
special_inside_parentheses
hash = {
key: :value
}
but_in_a_method_call({
its_like: :this
})
Example: EnforcedStyle: consistent
# The `consistent` style enforces that the first key in a hash
# literal where the opening brace and the first key are on
# seprate lines is indented the same as a hash literal which is not
# defined inside a method call.
# bad
hash = {
key: :value
}
but_in_a_method_call({
its_like: :this
})
# good
hash = {
key: :value
}
and_in_a_method_call({
no: :difference
})
Example: EnforcedStyle: align_braces
# The `align_brackets` style enforces that the opening and closing
# braces are indented to the same position.
# bad
and_now_for_something = {
completely: :different
}
# good
and_now_for_something = {
completely: :different
}
Unnecessary utf-8 encoding comment. Open
# encoding: utf-8
- Exclude checks
Gems should be sorted in an alphabetical order within their section of the Gemfile. Gem bower-rails
should appear before whenever
. Open
gem 'bower-rails', '~> 0.10.0'
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- Exclude checks
Gems should be alphabetically sorted within groups.
Example:
# bad
gem 'rubocop'
gem 'rspec'
# good
gem 'rspec'
gem 'rubocop'
# good
gem 'rubocop'
gem 'rspec'
# good only if TreatCommentsAsGroupSeparators is true
# For code quality
gem 'rubocop'
# For tests
gem 'rspec'
Line is too long. [98/80] Open
# The default locale is :en and all translations from config/locales/*.rb,yml are auto loaded.
- Exclude checks
Incorrect indentation detected (column 3 instead of 2). Open
# The priority is based upon order of creation: first created -> highest priority.
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- Exclude checks
This cops checks the indentation of comments.
Example:
# bad
# comment here
def method_name
end
# comment here
a = 'hello'
# yet another comment
if true
true
end
# good
# comment here
def method_name
end
# comment here
a = 'hello'
# yet another comment
if true
true
end
Line is too long. [85/80] Open
# The priority is based upon order of creation: first created -> highest priority.
- Exclude checks
Do not use spaces inside percent literal delimiters. Open
Rails.application.config.assets.precompile += %w( bootstrap/dist/js/bootstrap.js )
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- Exclude checks
Checks for unnecessary additional spaces inside the delimiters of %i/%w/%x literals.
Example:
# good
%i(foo bar baz)
# bad
%w( foo bar baz )
# bad
%x( ls -l )
Line is too long. [100/80] Open
# Set this to true and configure the email server for immediate delivery to raise delivery errors.
- Exclude checks
Unexpected console statement. Open
console.debug( "Wrapping the target-section" );
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- Exclude checks
disallow the use of console
(no-console)
In JavaScript that is designed to be executed in the browser, it's considered a best practice to avoid using methods on console
. Such messages are considered to be for debugging purposes and therefore not suitable to ship to the client. In general, calls using console
should be stripped before being pushed to production.
console.log("Made it here.");
console.error("That shouldn't have happened.");
Rule Details
This rule disallows calls to methods of the console
object.
Examples of incorrect code for this rule:
/*eslint no-console: "error"*/
console.log("Log a debug level message.");
console.warn("Log a warn level message.");
console.error("Log an error level message.");
Examples of correct code for this rule:
/*eslint no-console: "error"*/
// custom console
Console.log("Hello world!");
Options
This rule has an object option for exceptions:
-
"allow"
has an array of strings which are allowed methods of theconsole
object
Examples of additional correct code for this rule with a sample { "allow": ["warn", "error"] }
option:
/*eslint no-console: ["error", { allow: ["warn", "error"] }] */
console.warn("Log a warn level message.");
console.error("Log an error level message.");
When Not To Use It
If you're using Node.js, however, console
is used to output information to the user and so is not strictly used for debugging purposes. If you are developing for Node.js then you most likely do not want this rule enabled.
Related Rules
- [no-alert](no-alert.md)
- [no-debugger](no-debugger.md) Source: http://eslint.org/docs/rules/
Unexpected console statement. Open
console.debug( "Already wrapped." );
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- Exclude checks
disallow the use of console
(no-console)
In JavaScript that is designed to be executed in the browser, it's considered a best practice to avoid using methods on console
. Such messages are considered to be for debugging purposes and therefore not suitable to ship to the client. In general, calls using console
should be stripped before being pushed to production.
console.log("Made it here.");
console.error("That shouldn't have happened.");
Rule Details
This rule disallows calls to methods of the console
object.
Examples of incorrect code for this rule:
/*eslint no-console: "error"*/
console.log("Log a debug level message.");
console.warn("Log a warn level message.");
console.error("Log an error level message.");
Examples of correct code for this rule:
/*eslint no-console: "error"*/
// custom console
Console.log("Hello world!");
Options
This rule has an object option for exceptions:
-
"allow"
has an array of strings which are allowed methods of theconsole
object
Examples of additional correct code for this rule with a sample { "allow": ["warn", "error"] }
option:
/*eslint no-console: ["error", { allow: ["warn", "error"] }] */
console.warn("Log a warn level message.");
console.error("Log an error level message.");
When Not To Use It
If you're using Node.js, however, console
is used to output information to the user and so is not strictly used for debugging purposes. If you are developing for Node.js then you most likely do not want this rule enabled.
Related Rules
- [no-alert](no-alert.md)
- [no-debugger](no-debugger.md) Source: http://eslint.org/docs/rules/
'console' is not defined. Open
console.debug( "Highlighting click target for event %o", event.target );
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- Exclude checks
Disallow Undeclared Variables (no-undef)
This rule can help you locate potential ReferenceErrors resulting from misspellings of variable and parameter names, or accidental implicit globals (for example, from forgetting the var
keyword in a for
loop initializer).
Rule Details
Any reference to an undeclared variable causes a warning, unless the variable is explicitly mentioned in a /*global ...*/
comment.
Examples of incorrect code for this rule:
/*eslint no-undef: "error"*/
var a = someFunction();
b = 10;
Examples of correct code for this rule with global
declaration:
/*global someFunction b:true*/
/*eslint no-undef: "error"*/
var a = someFunction();
b = 10;
The b:true
syntax in /*global */
indicates that assignment to b
is correct.
Examples of incorrect code for this rule with global
declaration:
/*global b*/
/*eslint no-undef: "error"*/
b = 10;
By default, variables declared in /*global */
are read-only, therefore assignment is incorrect.
Options
-
typeof
set to true will warn for variables used inside typeof check (Default false).
typeof
Examples of correct code for the default { "typeof": false }
option:
/*eslint no-undef: "error"*/
if (typeof UndefinedIdentifier === "undefined") {
// do something ...
}
You can use this option if you want to prevent typeof
check on a variable which has not been declared.
Examples of incorrect code for the { "typeof": true }
option:
/*eslint no-undef: ["error", { "typeof": true }] */
if(typeof a === "string"){}
Examples of correct code for the { "typeof": true }
option with global
declaration:
/*global a*/
/*eslint no-undef: ["error", { "typeof": true }] */
if(typeof a === "string"){}
Environments
For convenience, ESLint provides shortcuts that pre-define global variables exposed by popular libraries and runtime environments. This rule supports these environments, as listed in Specifying Environments. A few examples are given below.
browser
Examples of correct code for this rule with browser
environment:
/*eslint no-undef: "error"*/
/*eslint-env browser*/
setTimeout(function() {
alert("Hello");
});
node
Examples of correct code for this rule with node
environment:
/*eslint no-undef: "error"*/
/*eslint-env node*/
var fs = require("fs");
module.exports = function() {
console.log(fs);
};
When Not To Use It
If explicit declaration of global variables is not to your taste.
Compatibility
This rule provides compatibility with treatment of global variables in JSHint and JSLint. Source: http://eslint.org/docs/rules/
'rdoc_rel_prefix' is not defined. Open
url: rdoc_rel_prefix + path,
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- Exclude checks
Disallow Undeclared Variables (no-undef)
This rule can help you locate potential ReferenceErrors resulting from misspellings of variable and parameter names, or accidental implicit globals (for example, from forgetting the var
keyword in a for
loop initializer).
Rule Details
Any reference to an undeclared variable causes a warning, unless the variable is explicitly mentioned in a /*global ...*/
comment.
Examples of incorrect code for this rule:
/*eslint no-undef: "error"*/
var a = someFunction();
b = 10;
Examples of correct code for this rule with global
declaration:
/*global someFunction b:true*/
/*eslint no-undef: "error"*/
var a = someFunction();
b = 10;
The b:true
syntax in /*global */
indicates that assignment to b
is correct.
Examples of incorrect code for this rule with global
declaration:
/*global b*/
/*eslint no-undef: "error"*/
b = 10;
By default, variables declared in /*global */
are read-only, therefore assignment is incorrect.
Options
-
typeof
set to true will warn for variables used inside typeof check (Default false).
typeof
Examples of correct code for the default { "typeof": false }
option:
/*eslint no-undef: "error"*/
if (typeof UndefinedIdentifier === "undefined") {
// do something ...
}
You can use this option if you want to prevent typeof
check on a variable which has not been declared.
Examples of incorrect code for the { "typeof": true }
option:
/*eslint no-undef: ["error", { "typeof": true }] */
if(typeof a === "string"){}
Examples of correct code for the { "typeof": true }
option with global
declaration:
/*global a*/
/*eslint no-undef: ["error", { "typeof": true }] */
if(typeof a === "string"){}
Environments
For convenience, ESLint provides shortcuts that pre-define global variables exposed by popular libraries and runtime environments. This rule supports these environments, as listed in Specifying Environments. A few examples are given below.
browser
Examples of correct code for this rule with browser
environment:
/*eslint no-undef: "error"*/
/*eslint-env browser*/
setTimeout(function() {
alert("Hello");
});
node
Examples of correct code for this rule with node
environment:
/*eslint no-undef: "error"*/
/*eslint-env node*/
var fs = require("fs");
module.exports = function() {
console.log(fs);
};
When Not To Use It
If explicit declaration of global variables is not to your taste.
Compatibility
This rule provides compatibility with treatment of global variables in JSHint and JSLint. Source: http://eslint.org/docs/rules/
Unexpected trailing comma. Open
searcher_loaded: false,
- Read upRead up
- Exclude checks
require or disallow trailing commas (comma-dangle)
Trailing commas in object literals are valid according to the ECMAScript 5 (and ECMAScript 3!) spec. However, IE8 (when not in IE8 document mode) and below will throw an error when it encounters trailing commas in JavaScript.
var foo = {
bar: "baz",
qux: "quux",
};
Trailing commas simplify adding and removing items to objects and arrays, since only the lines you are modifying must be touched. Another argument in favor of trailing commas is that it improves the clarity of diffs when an item is added or removed from an object or array:
Less clear:
var foo = {
- bar: "baz",
- qux: "quux"
+ bar: "baz"
};
More clear:
var foo = {
bar: "baz",
- qux: "quux",
};
Rule Details
This rule enforces consistent use of trailing commas in object and array literals.
Options
This rule has a string option or an object option:
{
"comma-dangle": ["error", "never"],
// or
"comma-dangle": ["error", {
"arrays": "never",
"objects": "never",
"imports": "never",
"exports": "never",
"functions": "ignore",
}]
}
-
"never"
(default) disallows trailing commas -
"always"
requires trailing commas -
"always-multiline"
requires trailing commas when the last element or property is in a different line than the closing]
or}
and disallows trailing commas when the last element or property is on the same line as the closing]
or}
-
"only-multiline"
allows (but does not require) trailing commas when the last element or property is in a different line than the closing]
or}
and disallows trailing commas when the last element or property is on the same line as the closing]
or}
Trailing commas in function declarations and function calls are valid syntax since ECMAScript 2017; however, the string option does not check these situations for backwards compatibility.
You can also use an object option to configure this rule for each type of syntax.
Each of the following options can be set to "never"
, "always"
, "always-multiline"
, "only-multiline"
, or "ignore"
.
The default for each option is "never"
unless otherwise specified.
-
arrays
is for array literals and array patterns of destructuring. (e.g.let [a,] = [1,];
) -
objects
is for object literals and object patterns of destructuring. (e.g.let {a,} = {a: 1};
) -
imports
is for import declarations of ES Modules. (e.g.import {a,} from "foo";
) -
exports
is for export declarations of ES Modules. (e.g.export {a,};
) -
functions
is for function declarations and function calls. (e.g.(function(a,){ })(b,);
)
functions
is set to"ignore"
by default for consistency with the string option.
never
Examples of incorrect code for this rule with the default "never"
option:
/*eslint comma-dangle: ["error", "never"]*/
var foo = {
bar: "baz",
qux: "quux",
};
var arr = [1,2,];
foo({
bar: "baz",
qux: "quux",
});
Examples of correct code for this rule with the default "never"
option:
/*eslint comma-dangle: ["error", "never"]*/
var foo = {
bar: "baz",
qux: "quux"
};
var arr = [1,2];
foo({
bar: "baz",
qux: "quux"
});
always
Examples of incorrect code for this rule with the "always"
option:
/*eslint comma-dangle: ["error", "always"]*/
var foo = {
bar: "baz",
qux: "quux"
};
var arr = [1,2];
foo({
bar: "baz",
qux: "quux"
});
Examples of correct code for this rule with the "always"
option:
/*eslint comma-dangle: ["error", "always"]*/
var foo = {
bar: "baz",
qux: "quux",
};
var arr = [1,2,];
foo({
bar: "baz",
qux: "quux",
});
always-multiline
Examples of incorrect code for this rule with the "always-multiline"
option:
/*eslint comma-dangle: ["error", "always-multiline"]*/
var foo = {
bar: "baz",
qux: "quux"
};
var foo = { bar: "baz", qux: "quux", };
var arr = [1,2,];
var arr = [1,
2,];
var arr = [
1,
2
];
foo({
bar: "baz",
qux: "quux"
});
Examples of correct code for this rule with the "always-multiline"
option:
/*eslint comma-dangle: ["error", "always-multiline"]*/
var foo = {
bar: "baz",
qux: "quux",
};
var foo = {bar: "baz", qux: "quux"};
var arr = [1,2];
var arr = [1,
2];
var arr = [
1,
2,
];
foo({
bar: "baz",
qux: "quux",
});
only-multiline
Examples of incorrect code for this rule with the "only-multiline"
option:
/*eslint comma-dangle: ["error", "only-multiline"]*/
var foo = { bar: "baz", qux: "quux", };
var arr = [1,2,];
var arr = [1,
2,];
Examples of correct code for this rule with the "only-multiline"
option:
/*eslint comma-dangle: ["error", "only-multiline"]*/
var foo = {
bar: "baz",
qux: "quux",
};
var foo = {
bar: "baz",
qux: "quux"
};
var foo = {bar: "baz", qux: "quux"};
var arr = [1,2];
var arr = [1,
2];
var arr = [
1,
2,
];
var arr = [
1,
2
];
foo({
bar: "baz",
qux: "quux",
});
foo({
bar: "baz",
qux: "quux"
});
functions
Examples of incorrect code for this rule with the {"functions": "never"}
option:
/*eslint comma-dangle: ["error", {"functions": "never"}]*/
function foo(a, b,) {
}
foo(a, b,);
new foo(a, b,);
Examples of correct code for this rule with the {"functions": "never"}
option:
/*eslint comma-dangle: ["error", {"functions": "never"}]*/
function foo(a, b) {
}
foo(a, b);
new foo(a, b);
Examples of incorrect code for this rule with the {"functions": "always"}
option:
/*eslint comma-dangle: ["error", {"functions": "always"}]*/
function foo(a, b) {
}
foo(a, b);
new foo(a, b);
Examples of correct code for this rule with the {"functions": "always"}
option:
/*eslint comma-dangle: ["error", {"functions": "always"}]*/
function foo(a, b,) {
}
foo(a, b,);
new foo(a, b,);
When Not To Use It
You can turn this rule off if you are not concerned with dangling commas. Source: http://eslint.org/docs/rules/
'$' is not defined. Open
this.$input = $(input);
- Read upRead up
- Exclude checks
Disallow Undeclared Variables (no-undef)
This rule can help you locate potential ReferenceErrors resulting from misspellings of variable and parameter names, or accidental implicit globals (for example, from forgetting the var
keyword in a for
loop initializer).
Rule Details
Any reference to an undeclared variable causes a warning, unless the variable is explicitly mentioned in a /*global ...*/
comment.
Examples of incorrect code for this rule:
/*eslint no-undef: "error"*/
var a = someFunction();
b = 10;
Examples of correct code for this rule with global
declaration:
/*global someFunction b:true*/
/*eslint no-undef: "error"*/
var a = someFunction();
b = 10;
The b:true
syntax in /*global */
indicates that assignment to b
is correct.
Examples of incorrect code for this rule with global
declaration:
/*global b*/
/*eslint no-undef: "error"*/
b = 10;
By default, variables declared in /*global */
are read-only, therefore assignment is incorrect.
Options
-
typeof
set to true will warn for variables used inside typeof check (Default false).
typeof
Examples of correct code for the default { "typeof": false }
option:
/*eslint no-undef: "error"*/
if (typeof UndefinedIdentifier === "undefined") {
// do something ...
}
You can use this option if you want to prevent typeof
check on a variable which has not been declared.
Examples of incorrect code for the { "typeof": true }
option:
/*eslint no-undef: ["error", { "typeof": true }] */
if(typeof a === "string"){}
Examples of correct code for the { "typeof": true }
option with global
declaration:
/*global a*/
/*eslint no-undef: ["error", { "typeof": true }] */
if(typeof a === "string"){}
Environments
For convenience, ESLint provides shortcuts that pre-define global variables exposed by popular libraries and runtime environments. This rule supports these environments, as listed in Specifying Environments. A few examples are given below.
browser
Examples of correct code for this rule with browser
environment:
/*eslint no-undef: "error"*/
/*eslint-env browser*/
setTimeout(function() {
alert("Hello");
});
node
Examples of correct code for this rule with node
environment:
/*eslint no-undef: "error"*/
/*eslint-env node*/
var fs = require("fs");
module.exports = function() {
console.log(fs);
};
When Not To Use It
If explicit declaration of global variables is not to your taste.
Compatibility
This rule provides compatibility with treatment of global variables in JSHint and JSLint. Source: http://eslint.org/docs/rules/
'suid' is assigned a value but never used. Open
var suid = 1;
- Read upRead up
- Exclude checks
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
orcommonjs
- when
parserOptions.sourceType
ismodule
- when
ecmaFeatures.globalReturn
istrue
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/
'jQuery' is not defined. Open
value = jQuery.trim(value).toLowerCase();
- Read upRead up
- Exclude checks
Disallow Undeclared Variables (no-undef)
This rule can help you locate potential ReferenceErrors resulting from misspellings of variable and parameter names, or accidental implicit globals (for example, from forgetting the var
keyword in a for
loop initializer).
Rule Details
Any reference to an undeclared variable causes a warning, unless the variable is explicitly mentioned in a /*global ...*/
comment.
Examples of incorrect code for this rule:
/*eslint no-undef: "error"*/
var a = someFunction();
b = 10;
Examples of correct code for this rule with global
declaration:
/*global someFunction b:true*/
/*eslint no-undef: "error"*/
var a = someFunction();
b = 10;
The b:true
syntax in /*global */
indicates that assignment to b
is correct.
Examples of incorrect code for this rule with global
declaration:
/*global b*/
/*eslint no-undef: "error"*/
b = 10;
By default, variables declared in /*global */
are read-only, therefore assignment is incorrect.
Options
-
typeof
set to true will warn for variables used inside typeof check (Default false).
typeof
Examples of correct code for the default { "typeof": false }
option:
/*eslint no-undef: "error"*/
if (typeof UndefinedIdentifier === "undefined") {
// do something ...
}
You can use this option if you want to prevent typeof
check on a variable which has not been declared.
Examples of incorrect code for the { "typeof": true }
option:
/*eslint no-undef: ["error", { "typeof": true }] */
if(typeof a === "string"){}
Examples of correct code for the { "typeof": true }
option with global
declaration:
/*global a*/
/*eslint no-undef: ["error", { "typeof": true }] */
if(typeof a === "string"){}
Environments
For convenience, ESLint provides shortcuts that pre-define global variables exposed by popular libraries and runtime environments. This rule supports these environments, as listed in Specifying Environments. A few examples are given below.
browser
Examples of correct code for this rule with browser
environment:
/*eslint no-undef: "error"*/
/*eslint-env browser*/
setTimeout(function() {
alert("Hello");
});
node
Examples of correct code for this rule with node
environment:
/*eslint no-undef: "error"*/
/*eslint-env node*/
var fs = require("fs");
module.exports = function() {
console.log(fs);
};
When Not To Use It
If explicit declaration of global variables is not to your taste.
Compatibility
This rule provides compatibility with treatment of global variables in JSHint and JSLint. Source: http://eslint.org/docs/rules/
Use %i
or %I
for an array of symbols. Open
COLLECTION_ATTRIBUTES = [
:project,
:id,
:created_at,
:updated_at,
- Read upRead up
- Exclude checks
This cop can check for array literals made up of symbols that are not using the %i() syntax.
Alternatively, it checks for symbol arrays using the %i() syntax on projects which do not want to use that syntax.
Configuration option: MinSize
If set, arrays with fewer elements than this value will not trigger the
cop. For example, a MinSize of
3` will not enforce a style on an array
of 2 or fewer elements.
Example: EnforcedStyle: percent (default)
# good
%i[foo bar baz]
# bad
[:foo, :bar, :baz]
Example: EnforcedStyle: brackets
# good
[:foo, :bar, :baz]
# bad
%i[foo bar baz]
Avoid comma after the last item of an array. Open
:updated_at,
- Read upRead up
- Exclude checks
This cop checks for trailing comma in array and hash literals.
Example: EnforcedStyleForMultiline: consistent_comma
# bad
a = [1, 2,]
# good
a = [
1, 2,
3,
]
# good
a = [
1,
2,
]
Example: EnforcedStyleForMultiline: comma
# bad
a = [1, 2,]
# good
a = [
1,
2,
]
Example: EnforcedStyleForMultiline: no_comma (default)
# bad
a = [1, 2,]
# good
a = [
1,
2
]