samples[studyId] = self.data.sampleLists.cna[studyId] || self.data.sampleLists.all[studyId]

Close

Enforce or Disallow Semicolons (semi)

(fixable) The --fix option on the [command line](../user-guide/command-line-interface#fix) automatically fixes problems reported by this rule.

JavaScript is unique amongst the C-like languages in that it doesn't require semicolons at the end of each statement. In many cases, the JavaScript engine can determine that a semicolon should be in a certain spot and will automatically add it. This feature is known as automatic semicolon insertion (ASI) and is considered one of the more controversial features of JavaScript. For example, the following lines are both valid:

var name = "ESLint"
var website = "eslint.org";

On the first line, the JavaScript engine will automatically insert a semicolon, so this is not considered a syntax error. The JavaScript engine still knows how to interpret the line and knows that the line end indicates the end of the statement.

In the debate over ASI, there are generally two schools of thought. The first is that we should treat ASI as if it didn't exist and always include semicolons manually. The rationale is that it's easier to always include semicolons than to try to remember when they are or are not required, and thus decreases the possibility of introducing an error.

However, the ASI mechanism can sometimes be tricky to people who are using semicolons. For example, consider this code:

return
{
    name: "ESLint"
};

This may look like a return statement that returns an object literal, however, the JavaScript engine will interpret this code as:

return;
{
    name: "ESLint";
}

Effectively, a semicolon is inserted after the return statement, causing the code below it (a labeled literal inside a block) to be unreachable. This rule and the [no-unreachable](no-unreachable.md) rule will protect your code from such cases.

On the other side of the argument are those who says that since semicolons are inserted automatically, they are optional and do not need to be inserted manually. However, the ASI mechanism can also be tricky to people who don't use semicolons. For example, consider this code:

var globalCounter = { }

(function () {
    var n = 0
    globalCounter.increment = function () {
        return ++n
    }
})()

In this example, a semicolon will not be inserted after the first line, causing a run-time error (because an empty object is called as if it's a function). The [no-unexpected-multiline](no-unexpected-multiline.md) rule can protect your code from such cases.

Although ASI allows for more freedom over your coding style, it can also make your code behave in an unexpected way, whether you use semicolons or not. Therefore, it is best to know when ASI takes place and when it does not, and have ESLint protect your code from these potentially unexpected cases. In short, as once described by Isaac Schlueter, a \n character always ends a statement (just like a semicolon) unless one of the following is true:

1. The statement has an unclosed paren, array literal, or object literal or ends in some other way that is not a valid way to end a statement. (For instance, ending with . or ,.)
2. The line is -- or ++ (in which case it will decrement/increment the next token.)
3. It is a for(), while(), do, if(), or else, and there is no {
4. The next line starts with [, (, +, *, /, -, ,, ., or some other binary operator that can only be found between two tokens in a single expression.

Rule Details

This rule is aimed at ensuring consistent use of semicolons. You can decide whether or not to require semicolons at the end of statements.

Options

The rule takes one or two options. The first one is a string, which could be "always" or "never". The default is "always". The second one is an object for more fine-grained configuration when the first option is "always".

You can set the option in configuration like this:

"always"

By using the default option, semicolons must be used any place where they are valid.

semi: ["error", "always"]

The following patterns are considered problems:

/*eslint semi: "error"*/

var name = "ESLint"

object.method = function() {
    // ...
}

The following patterns are not considered problems:

/*eslint semi: "error"*/

var name = "ESLint";

object.method = function() {
    // ...
};

Fine-grained control

When setting the first option as "always", an additional option can be added to omit the last semicolon in a one-line block, that is, a block in which its braces (and therefore the content of the block) are in the same line:

semi: ["error", "always", { "omitLastInOneLineBlock": true}]

The following patterns are considered problems:

/*eslint semi: ["error", "always", { "omitLastInOneLineBlock": true}] */

if (foo) {
    bar()
}

if (foo) { bar(); }

The following patterns are not considered problems:

/*eslint semi: ["error", "always", { "omitLastInOneLineBlock": true}] */

if (foo) { bar() }

if (foo) { bar(); baz() }

"never"

If you want to enforce that semicolons are never used, switch the configuration to:

semi: [2, "never"]

Then, the following patterns are considered problems:

/*eslint semi: ["error", "never"]*/

var name = "ESLint";

object.method = function() {
    // ...
};

And the following patterns are not considered problems:

/*eslint semi: ["error", "never"]*/

var name = "ESLint"

object.method = function() {
    // ...
}

Even in "never" mode, semicolons are still allowed to disambiguate statements beginning with [, (, /, +, or -:

/*eslint semi: ["error", "never"]*/

var name = "ESLint"

;(function() {
    // ...
})()

When Not To Use It

If you do not want to enforce semicolon usage (or omission) in any particular way, then you can turn this rule off.

Further Reading

• An Open Letter to JavaScript Leaders Regarding Semicolons
• JavaScript Semicolon Insertion
• Understanding Automatic Semicolon Insertion in JavaScript

Related Rules

• [no-extra-semi](no-extra-semi.md)
• [no-unexpected-multiline](no-unexpected-multiline.md)
• [semi-spacing](semi-spacing.md) Source: http://eslint.org/docs/rules/

            "sampleMolecularIdentifiers": map

Close

Enforce Quote Style (quotes)

(fixable) The --fix option on the [command line](../user-guide/command-line-interface#fix) automatically fixes problems reported by this rule.

JavaScript allows you to define strings in one of three ways: double quotes, single quotes, and backticks (as of ECMAScript 6). For example:

/*eslint-env es6*/

var double = "double";
var single = 'single';
var backtick = `backtick`;    // ES6 only

Each of these lines creates a string and, in some cases, can be used interchangeably. The choice of how to define strings in a codebase is a stylistic one outside of template literals (which allow embedded of expressions to be interpreted).

Many codebases require strings to be defined in a consistent manner.

Rule Details

This rule is aimed at ensuring consistency of string quotes and as such will report a problem when an inconsistent style is found.

The rule configuration takes up to two options:

1. The first option is "double", "single" or "backtick" for double-quotes, single-quotes or backticks respectively. The default is "double".
2. The second option takes two options:
   1. "avoidEscape": When using "avoidEscape", this rule will not report a problem when a string is using single-quotes or double-quotes so long as the string contains a quote that would have to be escaped otherwise. For example, if you specify "double" and "avoidEscape", the string 'He said, "hi!"' is not considered a problem because using double quotes for that string would require escaping the double quotes inside of the string. This option is off by default.
   2. "allowTemplateLiterals": when using "allowTemplateLiterals", this rule will not report a problem when a string is using backticks and option one is either "double" or "single".

When using "single" or "double", template literals that don't contain a substitution, don't contain a line break and aren't tagged templates, are flagged as problems, even with the "avoidEscape" option. However they are not problems when "allowTemplateLiterals" is used.

Configuration looks like this:

[2, "single", {"avoidEscape": true, "allowTemplateLiterals": true}]

Deprecation notice: The avoid-escape option is a deprecated syntax and you should use the object form instead.

The following patterns are considered problems:

/*eslint quotes: ["error", "double"]*/

var single = 'single';
var unescaped = 'a string containing "double" quotes';

/*eslint quotes: ["error", "single"]*/

var double = "double";
var unescaped = "a string containing 'single' quotes";

/*eslint quotes: ["error", "double", {"avoidEscape": true}]*/

var single = 'single';
var single = `single`;

/*eslint quotes: ["error", "single", {"avoidEscape": true}]*/

var double = "double";
var double = `double`;

/*eslint quotes: ["error", "backtick"]*/

var single = 'single';
var double = "double";
var unescaped = 'a string containing `backticks`';

/*eslint quotes: ["error", "backtick", {"avoidEscape": true}]*/

var single = 'single';
var double = "double";

The following patterns are not considered problems:

/*eslint quotes: ["error", "double"]*/
/*eslint-env es6*/

var double = "double";
var backtick = `back\ntick`;  // backticks are allowed due to newline
var backtick = tag`backtick`; // backticks are allowed due to tag

/*eslint quotes: ["error", "single"]*/
/*eslint-env es6*/

var single = 'single';
var backtick = `back${x}tick`; // backticks are allowed due to substitution

/*eslint quotes: ["error", "double", {"avoidEscape": true}]*/

var single = 'a string containing "double" quotes';

/*eslint quotes: ["error", "single", {"avoidEscape": true}]*/

var double = "a string containing 'single' quotes";

/*eslint quotes: ["error", "double", {"allowTemplateLiterals": true}]*/

var single = 'single';
var single = `single`;

/*eslint quotes: ["error", "single", {"allowTemplateLiterals": true}]*/

var double = "double";
var double = `double`;

/*eslint quotes: ["error", "backtick"]*/
/*eslint-env es6*/

var backtick = `backtick`;

/*eslint quotes: ["error", "backtick", {"avoidEscape": true}]*/

var double = "a string containing `backtick` quotes"

When Not To Use It

If you do not need consistency in your string styles, you can safely disable this rule. Source: http://eslint.org/docs/rules/

            } else if (_filter.viewType === 'scatter_plot' || _filter.viewType === 'custom') {

Close

enforce a maximum line length (max-len)

Very long lines of code in any language can be difficult to read. In order to aid in readability and maintainability many coders have developed a convention to limit lines of code to X number of characters (traditionally 80 characters).

var foo = { "bar": "This is a bar.", "baz": { "qux": "This is a qux" }, "difficult": "to read" }; // very long

Rule Details

This rule enforces a maximum line length to increase code readability and maintainability.

Note: This rule calculates the length of a line via code points, not characters. That means if you use a double-byte character in your code, it will count as 2 code points instead of 1, and 2 will be used to calculate line length. This is a technical limitation of JavaScript that is made easier with ES2015, and we will look to update this when ES2015 is available in Node.js.

Options

This rule has a number or object option:

• "code" (default 80) enforces a maximum line length
• "tabWidth" (default 4) specifies the character width for tab characters
• "comments" enforces a maximum line length for comments; defaults to value of code
• "ignorePattern" ignores lines matching a regular expression; can only match a single line and need to be double escaped when written in YAML or JSON
• "ignoreComments": true ignores all trailing comments and comments on their own line
• "ignoreTrailingComments": true ignores only trailing comments
• "ignoreUrls": true ignores lines that contain a URL

code

Examples of incorrect code for this rule with the default { "code": 80 } option:

/*eslint max-len: ["error", 80]*/

var foo = { "bar": "This is a bar.", "baz": { "qux": "This is a qux" }, "difficult": "to read" };

Examples of correct code for this rule with the default { "code": 80 } option:

/*eslint max-len: ["error", 80]*/

var foo = {
  "bar": "This is a bar.",
  "baz": { "qux": "This is a qux" },
  "easier": "to read"
};

tabWidth

Examples of incorrect code for this rule with the default { "tabWidth": 4 } option:

/*eslint max-len: ["error", 80, 4]*/

\t  \t  var foo = { "bar": "This is a bar.", "baz": { "qux": "This is a qux" } };

Examples of correct code for this rule with the default { "tabWidth": 4 } option:

/*eslint max-len: ["error", 80, 4]*/

\t  \t  var foo = {
\t  \t  \t  \t  "bar": "This is a bar.",
\t  \t  \t  \t  "baz": { "qux": "This is a qux" }
\t  \t  };

comments

Examples of incorrect code for this rule with the { "comments": 65 } option:

/*eslint max-len: ["error", { "comments": 65 }]*/

/**
 * This is a comment that violates the maximum line length we have specified
**/

ignoreComments

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

/*eslint max-len: ["error", { "ignoreComments": true }]*/

/**
 * This is a really really really really really really really really really long comment
**/

ignoreTrailingComments

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

/*eslint max-len: ["error", { "ignoreTrailingComments": true }]*/

var foo = 'bar'; // This is a really really really really really really really long comment

ignoreUrls

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

/*eslint max-len: ["error", { "ignoreUrls": true }]*/

var url = 'https://www.example.com/really/really/really/really/really/really/really/long';

ignorePattern

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

/*eslint max-len: ["error", { "ignorePattern": "^\\s*var\\s.+=\\s*require\\s*\\(/" }]*/

var dep = require('really/really/really/really/really/really/really/really/long/module');

Related Rules

• [complexity](complexity.md)
• [max-depth](max-depth.md)
• [max-nested-callbacks](max-nested-callbacks.md)
• [max-params](max-params.md)
• [max-statements](max-statements.md) Source: http://eslint.org/docs/rules/

              if (selectedNumBar[0] >= opts_.xDomain[i + 1] && selectedNumBar[0] < opts_.xDomain[i + 2]) {

Close

enforce a maximum line length (max-len)

Very long lines of code in any language can be difficult to read. In order to aid in readability and maintainability many coders have developed a convention to limit lines of code to X number of characters (traditionally 80 characters).

var foo = { "bar": "This is a bar.", "baz": { "qux": "This is a qux" }, "difficult": "to read" }; // very long

Rule Details

This rule enforces a maximum line length to increase code readability and maintainability.

Note: This rule calculates the length of a line via code points, not characters. That means if you use a double-byte character in your code, it will count as 2 code points instead of 1, and 2 will be used to calculate line length. This is a technical limitation of JavaScript that is made easier with ES2015, and we will look to update this when ES2015 is available in Node.js.

Options

This rule has a number or object option:

• "code" (default 80) enforces a maximum line length
• "tabWidth" (default 4) specifies the character width for tab characters
• "comments" enforces a maximum line length for comments; defaults to value of code
• "ignorePattern" ignores lines matching a regular expression; can only match a single line and need to be double escaped when written in YAML or JSON
• "ignoreComments": true ignores all trailing comments and comments on their own line
• "ignoreTrailingComments": true ignores only trailing comments
• "ignoreUrls": true ignores lines that contain a URL

code

Examples of incorrect code for this rule with the default { "code": 80 } option:

/*eslint max-len: ["error", 80]*/

var foo = { "bar": "This is a bar.", "baz": { "qux": "This is a qux" }, "difficult": "to read" };

Examples of correct code for this rule with the default { "code": 80 } option:

/*eslint max-len: ["error", 80]*/

var foo = {
  "bar": "This is a bar.",
  "baz": { "qux": "This is a qux" },
  "easier": "to read"
};

tabWidth

Examples of incorrect code for this rule with the default { "tabWidth": 4 } option:

/*eslint max-len: ["error", 80, 4]*/

\t  \t  var foo = { "bar": "This is a bar.", "baz": { "qux": "This is a qux" } };

Examples of correct code for this rule with the default { "tabWidth": 4 } option:

/*eslint max-len: ["error", 80, 4]*/

\t  \t  var foo = {
\t  \t  \t  \t  "bar": "This is a bar.",
\t  \t  \t  \t  "baz": { "qux": "This is a qux" }
\t  \t  };

comments

Examples of incorrect code for this rule with the { "comments": 65 } option:

/*eslint max-len: ["error", { "comments": 65 }]*/

/**
 * This is a comment that violates the maximum line length we have specified
**/

ignoreComments

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

/*eslint max-len: ["error", { "ignoreComments": true }]*/

/**
 * This is a really really really really really really really really really long comment
**/

ignoreTrailingComments

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

/*eslint max-len: ["error", { "ignoreTrailingComments": true }]*/

var foo = 'bar'; // This is a really really really really really really really long comment

ignoreUrls

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

/*eslint max-len: ["error", { "ignoreUrls": true }]*/

var url = 'https://www.example.com/really/really/really/really/really/really/really/long';

ignorePattern

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

/*eslint max-len: ["error", { "ignorePattern": "^\\s*var\\s.+=\\s*require\\s*\\(/" }]*/

var dep = require('really/really/really/really/really/really/really/really/long/module');

Related Rules

• [complexity](complexity.md)
• [max-depth](max-depth.md)
• [max-nested-callbacks](max-nested-callbacks.md)
• [max-params](max-params.md)
• [max-statements](max-statements.md) Source: http://eslint.org/docs/rules/

          if (data_.noGrouping) {

Close

Disallow if as the Only Statement in an else Block (no-lonely-if)

If an if statement is the only statement in the else block of a parent if statement, it is often clearer to combine the two to using else if form.

if (foo) {
    // ...
} else {
    if (bar) {
        // ...
    }
}

should be rewritten as

if (foo) {
    // ...
} else if (bar) {
    // ...
}

Rule Details

This rule warns when an if statement's else block contains only another if statement.

The following patterns are considered problems:

/*eslint no-lonely-if: "error"*/

if (condition) {
    // ...
} else {
    if (anotherCondition) {
        // ...
    }
}

if (condition) {
    // ...
} else {
    if (anotherCondition) {
        // ...
    } else {
        // ...
    }
}

The following patterns are not considered problems:

/*eslint no-lonely-if: "error"*/

if (condition) {
    // ...
} else if (anotherCondition) {
    // ...
}

if (condition) {
    // ...
} else if (anotherCondition) {
    // ...
} else {
    // ...
}

if (condition) {
    // ...
} else {
    if (anotherCondition) {
        // ...
    }
    doSomething();
}

When Not To Use It

Disable this rule if the code is clearer without requiring the else if form. Source: http://eslint.org/docs/rules/

      var selectedCases = _.pluck(dcDimension.top(Infinity), groupTypeId).sort();

Close

enforce a maximum line length (max-len)

Very long lines of code in any language can be difficult to read. In order to aid in readability and maintainability many coders have developed a convention to limit lines of code to X number of characters (traditionally 80 characters).

var foo = { "bar": "This is a bar.", "baz": { "qux": "This is a qux" }, "difficult": "to read" }; // very long

Rule Details

This rule enforces a maximum line length to increase code readability and maintainability.

Note: This rule calculates the length of a line via code points, not characters. That means if you use a double-byte character in your code, it will count as 2 code points instead of 1, and 2 will be used to calculate line length. This is a technical limitation of JavaScript that is made easier with ES2015, and we will look to update this when ES2015 is available in Node.js.

Options

This rule has a number or object option:

• "code" (default 80) enforces a maximum line length
• "tabWidth" (default 4) specifies the character width for tab characters
• "comments" enforces a maximum line length for comments; defaults to value of code
• "ignorePattern" ignores lines matching a regular expression; can only match a single line and need to be double escaped when written in YAML or JSON
• "ignoreComments": true ignores all trailing comments and comments on their own line
• "ignoreTrailingComments": true ignores only trailing comments
• "ignoreUrls": true ignores lines that contain a URL

code

Examples of incorrect code for this rule with the default { "code": 80 } option:

/*eslint max-len: ["error", 80]*/

var foo = { "bar": "This is a bar.", "baz": { "qux": "This is a qux" }, "difficult": "to read" };

Examples of correct code for this rule with the default { "code": 80 } option:

/*eslint max-len: ["error", 80]*/

var foo = {
  "bar": "This is a bar.",
  "baz": { "qux": "This is a qux" },
  "easier": "to read"
};

tabWidth

Examples of incorrect code for this rule with the default { "tabWidth": 4 } option:

/*eslint max-len: ["error", 80, 4]*/

\t  \t  var foo = { "bar": "This is a bar.", "baz": { "qux": "This is a qux" } };

Examples of correct code for this rule with the default { "tabWidth": 4 } option:

/*eslint max-len: ["error", 80, 4]*/

\t  \t  var foo = {
\t  \t  \t  \t  "bar": "This is a bar.",
\t  \t  \t  \t  "baz": { "qux": "This is a qux" }
\t  \t  };

comments

Examples of incorrect code for this rule with the { "comments": 65 } option:

/*eslint max-len: ["error", { "comments": 65 }]*/

/**
 * This is a comment that violates the maximum line length we have specified
**/

ignoreComments

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

/*eslint max-len: ["error", { "ignoreComments": true }]*/

/**
 * This is a really really really really really really really really really long comment
**/

ignoreTrailingComments

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

/*eslint max-len: ["error", { "ignoreTrailingComments": true }]*/

var foo = 'bar'; // This is a really really really really really really really long comment

ignoreUrls

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

/*eslint max-len: ["error", { "ignoreUrls": true }]*/

var url = 'https://www.example.com/really/really/really/really/really/really/really/long';

ignorePattern

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

/*eslint max-len: ["error", { "ignorePattern": "^\\s*var\\s.+=\\s*require\\s*\\(/" }]*/

var dep = require('really/really/really/really/really/really/really/really/long/module');

Related Rules

• [complexity](complexity.md)
• [max-depth](max-depth.md)
• [max-nested-callbacks](max-nested-callbacks.md)
• [max-params](max-params.md)
• [max-statements](max-statements.md) Source: http://eslint.org/docs/rules/

    'value="sample" checked @click="clearCaseIds(\'sample\')">By sample ID</label><label><input type="radio" ' +

Close

enforce a maximum line length (max-len)

Very long lines of code in any language can be difficult to read. In order to aid in readability and maintainability many coders have developed a convention to limit lines of code to X number of characters (traditionally 80 characters).

var foo = { "bar": "This is a bar.", "baz": { "qux": "This is a qux" }, "difficult": "to read" }; // very long

Rule Details

This rule enforces a maximum line length to increase code readability and maintainability.

Note: This rule calculates the length of a line via code points, not characters. That means if you use a double-byte character in your code, it will count as 2 code points instead of 1, and 2 will be used to calculate line length. This is a technical limitation of JavaScript that is made easier with ES2015, and we will look to update this when ES2015 is available in Node.js.

Options

This rule has a number or object option:

• "code" (default 80) enforces a maximum line length
• "tabWidth" (default 4) specifies the character width for tab characters
• "comments" enforces a maximum line length for comments; defaults to value of code
• "ignorePattern" ignores lines matching a regular expression; can only match a single line and need to be double escaped when written in YAML or JSON
• "ignoreComments": true ignores all trailing comments and comments on their own line
• "ignoreTrailingComments": true ignores only trailing comments
• "ignoreUrls": true ignores lines that contain a URL

code

Examples of incorrect code for this rule with the default { "code": 80 } option:

/*eslint max-len: ["error", 80]*/

var foo = { "bar": "This is a bar.", "baz": { "qux": "This is a qux" }, "difficult": "to read" };

Examples of correct code for this rule with the default { "code": 80 } option:

/*eslint max-len: ["error", 80]*/

var foo = {
  "bar": "This is a bar.",
  "baz": { "qux": "This is a qux" },
  "easier": "to read"
};

tabWidth

Examples of incorrect code for this rule with the default { "tabWidth": 4 } option:

/*eslint max-len: ["error", 80, 4]*/

\t  \t  var foo = { "bar": "This is a bar.", "baz": { "qux": "This is a qux" } };

Examples of correct code for this rule with the default { "tabWidth": 4 } option:

/*eslint max-len: ["error", 80, 4]*/

\t  \t  var foo = {
\t  \t  \t  \t  "bar": "This is a bar.",
\t  \t  \t  \t  "baz": { "qux": "This is a qux" }
\t  \t  };

comments

Examples of incorrect code for this rule with the { "comments": 65 } option:

/*eslint max-len: ["error", { "comments": 65 }]*/

/**
 * This is a comment that violates the maximum line length we have specified
**/

ignoreComments

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

/*eslint max-len: ["error", { "ignoreComments": true }]*/

/**
 * This is a really really really really really really really really really long comment
**/

ignoreTrailingComments

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

/*eslint max-len: ["error", { "ignoreTrailingComments": true }]*/

var foo = 'bar'; // This is a really really really really really really really long comment

ignoreUrls

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

/*eslint max-len: ["error", { "ignoreUrls": true }]*/

var url = 'https://www.example.com/really/really/really/really/really/really/really/long';

ignorePattern

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

/*eslint max-len: ["error", { "ignorePattern": "^\\s*var\\s.+=\\s*require\\s*\\(/" }]*/

var dep = require('really/really/really/really/really/really/really/really/long/module');

Related Rules

• [complexity](complexity.md)
• [max-depth](max-depth.md)
• [max-nested-callbacks](max-nested-callbacks.md)
• [max-params](max-params.md)
• [max-statements](max-statements.md) Source: http://eslint.org/docs/rules/

        return cases.join('\n');;

Close

disallow unreachable code after return, throw, continue, and break statements (no-unreachable)

Because the return, throw, break, and continue statements unconditionally exit a block of code, any statements after them cannot be executed. Unreachable statements are usually a mistake.

function fn() {
    x = 1;
    return x;
    x = 3; // this will never execute
}

Rule Details

This rule disallows unreachable code after return, throw, continue, and break statements.

Examples of incorrect code for this rule:

/*eslint no-unreachable: "error"*/

function foo() {
    return true;
    console.log("done");
}

function bar() {
    throw new Error("Oops!");
    console.log("done");
}

while(value) {
    break;
    console.log("done");
}

throw new Error("Oops!");
console.log("done");

function baz() {
    if (Math.random() < 0.5) {
        return;
    } else {
        throw new Error();
    }
    console.log("done");
}

for (;;) {}
console.log("done");

Examples of correct code for this rule, because of JavaScript function and variable hoisting:

/*eslint no-unreachable: "error"*/

function foo() {
    return bar();
    function bar() {
        return 1;
    }
}

function bar() {
    return x;
    var x;
}

switch (foo) {
    case 1:
        break;
        var x;
}

Source: http://eslint.org/docs/rules/

            if (typeof genePanelMap[item.gene] !== 'undefined') {

Close

Disallow use of negated expressions in conditions (no-negated-condition)

Checks against the use of a negated expression in an if condition when the else branch is not empty or in a ternary operator. Negated conditions are more difficult to understand. Code can be made more readable by inverting the condition instead.

For example:

if (!a) {
    doSomething();
}
else {
    doSomethingElse();
}

should instead be written as:

if (a) {
    doSomethingElse();
}
else {
    doSomething();
}

Rule Details

The rule is aimed at preventing the use of a negated expression in a condition.

The following patterns are considered warnings:

/*eslint no-negated-condition: "error"*/

if (!a) {
    doSomething();
} else {
    doSomethingElse();
}

if (a != b) {
    doSomething();
} else {
    doSomethingElse();
}

if (a !== b) {
    doSomething();
} else {
    doSomethingElse();
}


!a ? b : c

The following patterns are not warnings:

/*eslint no-negated-condition: "error"*/

if (!a) {
    doSomething();
}

if (!a) {
    doSomething();
} else if (b) {
    doSomething();
}

if (a != b) {
    doSomething();
}

a ? b : c

Source: http://eslint.org/docs/rules/

    function reactRowClickCallback(data, selected) {

Close

Require JSDoc comment (require-jsdoc)

JSDoc is a JavaScript API documentation generator. It uses specially-formatted comments inside of code to generate API documentation automatically. For example, this is what a JSDoc comment looks like for a function:

/**
 * Adds two numbers together.
 * @param {int} num1 The first number.
 * @param {int} num2 The second number.
 * @returns {int} The sum of the two numbers.
 */
function sum(num1, num2) {
    return num1 + num2;
}

Some style guides require JSDoc comments for all functions as a way of explaining function behavior.

Rule Details

This rule generates warnings for nodes that do not have JSDoc comments when they should. Supported nodes:

• FunctionDeclaration
• ClassDeclaration
• MethodDefinition

Options

This rule accepts a require object with its properties as

• FunctionDeclaration (default: true)
• ClassDeclaration (default: false)
• MethodDefinition (default: false)

Default option settings are

{
    "require-jsdoc": ["error", {
        "require": {
            "FunctionDeclaration": true,
            "MethodDefinition": false,
            "ClassDeclaration": false
        }
    }]
}

The following patterns are considered problems:

/*eslint "require-jsdoc": ["error", {
    "require": {
        "FunctionDeclaration": true,
        "MethodDefinition": true,
        "ClassDeclaration": true
    }
}]*/

function foo() {
    return 10;
}

class Test{
    getDate(){}
}

The following patterns are not considered problems:

/*eslint "require-jsdoc": ["error", {
    "require": {
        "FunctionDeclaration": true,
        "MethodDefinition": true,
        "ClassDeclaration": true
    }
}]*/

/**
* It returns 10
*/
function foo() {
    return 10;
}

/**
* It returns 10
*/
var foo = function() {
    return 10;
}

var array = [1,2,3];
array.filter(function(item) {
    return item > 2;
});

/**
* It returns 10
*/
class Test{
    /**
    * returns the date
    */
    getDate(){}
}

When Not To Use It

If you do not require JSDoc for your functions, then you can leave this rule off.

Related Rules

• [valid-jsdoc](valid-jsdoc.md) Source: http://eslint.org/docs/rules/

          if(this.chartFilters.length === 0) {

Close

enforce consistent spacing before and after keywords (keyword-spacing)

(fixable) The --fix option on the [command line](../user-guide/command-line-interface#fix) automatically fixes problems reported by this rule.

Keywords are syntax elements of JavaScript, such as function and if. These identifiers have special meaning to the language and so often appear in a different color in code editors. As an important part of the language, style guides often refer to the spacing that should be used around keywords. For example, you might have a style guide that says keywords should be always surrounded by spaces, which would mean if-else statements must look like this:

if (foo) {
    // ...
} else {
    // ...
}

Of course, you could also have a style guide that disallows spaces around keywords.

Rule Details

This rule enforces consistent spacing around keywords and keyword-like tokens: as (in module declarations), break, case, catch, class, const, continue, debugger, default, delete, do, else, export, extends, finally, for, from (in module declarations), function, get (of getters), if, import, in, instanceof, let, new, of (in for-of statements), return, set (of setters), static, super, switch, this, throw, try, typeof, var, void, while, with, and yield. This rule is designed carefully not to conflict with other spacing rules: it does not apply to spacing where other rules report problems.

Options

This rule has an object option:

• "before": true (default) requires at least one space before keywords
• "before": false disallows spaces before keywords
• "after": true (default) requires at least one space after keywords
• "after": false disallows spaces after keywords
• "overrides" allows overriding spacing style for specified keywords

before

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

/*eslint keyword-spacing: ["error", { "before": true }]*/

if (foo) {
    //...
}else if (bar) {
    //...
}else {
    //...
}

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

/*eslint keyword-spacing: ["error", { "before": true }]*/
/*eslint-env es6*/

if (foo) {
    //...
} else if (bar) {
    //...
} else {
    //...
}

// no conflict with `array-bracket-spacing`
let a = [this];
let b = [function() {}];

// no conflict with `arrow-spacing`
let a = ()=> this.foo;

// no conflict with `block-spacing`
{function foo() {}}

// no conflict with `comma-spacing`
let a = [100,this.foo, this.bar];

// not conflict with `computed-property-spacing`
obj[this.foo] = 0;

// no conflict with `generator-star-spacing`
function *foo() {}

// no conflict with `key-spacing`
let obj = {
    foo:function() {}
};

// no conflict with `object-curly-spacing`
let obj = {foo: this};

// no conflict with `semi-spacing`
let a = this;function foo() {}

// no conflict with `space-in-parens`
(function () {})();

// no conflict with `space-infix-ops`
if ("foo"in {foo: 0}) {}
if (10+this.foo<= this.bar) {}

// no conflict with `jsx-curly-spacing`
let a = 

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

/*eslint keyword-spacing: ["error", { "before": false }]*/

if (foo) {
    //...
} else if (bar) {
    //...
} else {
    //...
}

Examples of correct code for this rule with the { "before": false } option:

/*eslint keyword-spacing: ["error", { "before": false }]*/

if (foo) {
    //...
}else if (bar) {
    //...
}else {
    //...
}

after

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

/*eslint keyword-spacing: ["error", { "after": true }]*/

if(foo) {
    //...
} else if(bar) {
    //...
} else{
    //...
}

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

/*eslint keyword-spacing: ["error", { "after": true }]*/

if (foo) {
    //...
} else if (bar) {
    //...
} else {
    //...
}

// not conflict with `array-bracket-spacing`
let a = [this];

// not conflict with `arrow-spacing`
let a = ()=> this.foo;

// not conflict with `comma-spacing`
let a = [100, this.foo, this.bar];

// not conflict with `computed-property-spacing`
obj[this.foo] = 0;

// not conflict with `generator-star-spacing`
function* foo() {}

// not conflict with `key-spacing`
let obj = {
    foo:function() {}
};

// not conflict with `no-spaced-func`
class A {
    constructor() {
        super();
    }
}

// not conflict with `object-curly-spacing`
let obj = {foo: this};

// not conflict with `semi-spacing`
let a = this;function foo() {}

// not conflict with `space-before-function-paren`
function() {}

// no conflict with `space-infix-ops`
if ("foo"in{foo: 0}) {}
if (10+this.foo<= this.bar) {}

// no conflict with `space-unary-ops`
function* foo(a) {
    return yield+a;
}

// no conflict with `yield-star-spacing`
function* foo(a) {
    return yield* a;
}

// no conflict with `jsx-curly-spacing`
let a = 

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

/*eslint keyword-spacing: ["error", { "after": false }]*/

if (foo) {
    //...
} else if (bar) {
    //...
} else {
    //...
}

Examples of correct code for this rule with the { "after": false } option:

/*eslint keyword-spacing: ["error", { "after": false }]*/

if(foo) {
    //...
} else if(bar) {
    //...
} else{
    //...
}

overrides

Examples of correct code for this rule with the { "overrides": { "if": { "after": false }, "for": { "after": false }, "while": { "after": false } } } option:

/*eslint keyword-spacing: ["error", { "overrides": {
  "if": { "after": false },
  "for": { "after": false },
  "while": { "after": false }
} }]*/

if(foo) {
    //...
} else if(bar) {
    //...
} else {
    //...
}

for(;;);

while(true) {
  //...
}

When Not To Use It

If you don't want to enforce consistency on keyword spacing, then it's safe to disable this rule. Source: http://eslint.org/docs/rules/

    function updateReactTable() {

Close

Require JSDoc comment (require-jsdoc)

JSDoc is a JavaScript API documentation generator. It uses specially-formatted comments inside of code to generate API documentation automatically. For example, this is what a JSDoc comment looks like for a function:

/**
 * Adds two numbers together.
 * @param {int} num1 The first number.
 * @param {int} num2 The second number.
 * @returns {int} The sum of the two numbers.
 */
function sum(num1, num2) {
    return num1 + num2;
}

Some style guides require JSDoc comments for all functions as a way of explaining function behavior.

Rule Details

This rule generates warnings for nodes that do not have JSDoc comments when they should. Supported nodes:

• FunctionDeclaration
• ClassDeclaration
• MethodDefinition

Options

This rule accepts a require object with its properties as

• FunctionDeclaration (default: true)
• ClassDeclaration (default: false)
• MethodDefinition (default: false)

Default option settings are

{
    "require-jsdoc": ["error", {
        "require": {
            "FunctionDeclaration": true,
            "MethodDefinition": false,
            "ClassDeclaration": false
        }
    }]
}

The following patterns are considered problems:

/*eslint "require-jsdoc": ["error", {
    "require": {
        "FunctionDeclaration": true,
        "MethodDefinition": true,
        "ClassDeclaration": true
    }
}]*/

function foo() {
    return 10;
}

class Test{
    getDate(){}
}

The following patterns are not considered problems:

/*eslint "require-jsdoc": ["error", {
    "require": {
        "FunctionDeclaration": true,
        "MethodDefinition": true,
        "ClassDeclaration": true
    }
}]*/

/**
* It returns 10
*/
function foo() {
    return 10;
}

/**
* It returns 10
*/
var foo = function() {
    return 10;
}

var array = [1,2,3];
array.filter(function(item) {
    return item > 2;
});

/**
* It returns 10
*/
class Test{
    /**
    * returns the date
    */
    getDate(){}
}

When Not To Use It

If you do not require JSDoc for your functions, then you can leave this rule off.

Related Rules

• [valid-jsdoc](valid-jsdoc.md) Source: http://eslint.org/docs/rules/

    function drawMarker(_slice) {

Close

Require JSDoc comment (require-jsdoc)

JSDoc is a JavaScript API documentation generator. It uses specially-formatted comments inside of code to generate API documentation automatically. For example, this is what a JSDoc comment looks like for a function:

/**
 * Adds two numbers together.
 * @param {int} num1 The first number.
 * @param {int} num2 The second number.
 * @returns {int} The sum of the two numbers.
 */
function sum(num1, num2) {
    return num1 + num2;
}

Some style guides require JSDoc comments for all functions as a way of explaining function behavior.

Rule Details

This rule generates warnings for nodes that do not have JSDoc comments when they should. Supported nodes:

• FunctionDeclaration
• ClassDeclaration
• MethodDefinition

Options

This rule accepts a require object with its properties as

• FunctionDeclaration (default: true)
• ClassDeclaration (default: false)
• MethodDefinition (default: false)

Default option settings are

{
    "require-jsdoc": ["error", {
        "require": {
            "FunctionDeclaration": true,
            "MethodDefinition": false,
            "ClassDeclaration": false
        }
    }]
}

The following patterns are considered problems:

/*eslint "require-jsdoc": ["error", {
    "require": {
        "FunctionDeclaration": true,
        "MethodDefinition": true,
        "ClassDeclaration": true
    }
}]*/

function foo() {
    return 10;
}

class Test{
    getDate(){}
}

The following patterns are not considered problems:

/*eslint "require-jsdoc": ["error", {
    "require": {
        "FunctionDeclaration": true,
        "MethodDefinition": true,
        "ClassDeclaration": true
    }
}]*/

/**
* It returns 10
*/
function foo() {
    return 10;
}

/**
* It returns 10
*/
var foo = function() {
    return 10;
}

var array = [1,2,3];
array.filter(function(item) {
    return item > 2;
});

/**
* It returns 10
*/
class Test{
    /**
    * returns the date
    */
    getDate(){}
}

When Not To Use It

If you do not require JSDoc for your functions, then you can leave this rule off.

Related Rules

• [valid-jsdoc](valid-jsdoc.md) Source: http://eslint.org/docs/rules/

    watch: {

Close

Quoting Style for Property Names (quote-props)

Object literal property names can be defined in two ways: using literals or using strings. For example, these two objects are equivalent:

var object1 = {
    property: true
};

var object2 = {
    "property": true
};

In many cases, it doesn't matter if you choose to use an identifier instead of a string or vice-versa. Even so, you might decide to enforce a consistent style in your code.

There are, however, some occasions when you must use quotes:

1. If you are using an ECMAScript 3 JavaScript engine (such as IE8) and you want to use a keyword (such as if) as a property name. This restriction was removed in ECMAScript 5.
2. You want to use a non-identifier character in your property name, such as having a property with a space like "one two".

Another example where quotes do matter is when using numeric literals as property keys:

var object = {
    1e2: 1,
    100: 2
};

This may look alright at first sight, but this code in fact throws a syntax error in ECMAScript 5 strict mode. This happens because 1e2 and 100 are coerced into strings before getting used as the property name. Both String(1e2) and String(100) happen to be equal to "100", which causes the "Duplicate data property in object literal not allowed in strict mode" error. Issues like that can be tricky to debug, so some prefer to require quotes around all property names.

Rule Details

This rule aims to enforce use of quotes in property names and as such will flag any properties that don't use quotes (default behavior).

Options

There are four behaviors for this rule: "always" (default), "as-needed", "consistent" and "consistent-as-needed". You can define these options in your configuration as:

{
    "quote-props": ["error", "as-needed"]
}

"always"

When configured with "always" as the first option (the default), quoting for all properties will be enforced. Some believe that ensuring property names in object literals are always wrapped in quotes is generally a good idea, since depending on the property name you may need to quote them anyway. Consider this example:

var object = {
    foo: "bar",
    baz: 42,
    "qux-lorem": true
};

Here, the properties foo and baz are not wrapped in quotes, but qux-lorem is, because it doesn’t work without the quotes. This is rather inconsistent. Instead, you may prefer to quote names of all properties:

var object = {
    "foo": "bar",
    "baz": 42,
    "qux-lorem": true
};

or, if you prefer single quotes:

var object = {
    'foo': 'bar',
    'baz': 42,
    'qux-lorem': true
};

When configured with "always" as the first option (the default), quoting for all properties will be enforced. The following patterns are considered problems:

/*eslint quote-props: ["error", "always"]*/

var object = {
    foo: "bar",
    baz: 42,
    "qux-lorem": true
};

The following patterns are not considered problems:

/*eslint quote-props: ["error", "always"]*/
/*eslint-env es6*/

var object1 = {
    "foo": "bar",
    "baz": 42,
    "qux-lorem": true
};

var object2 = {
    'foo': 'bar',
    'baz': 42,
    'qux-lorem': true
};

var object3 = {
    foo() {
        return;
    }
};

"as-needed"

When configured with "as-needed" as the first option, quotes will be enforced when they are strictly required, and unnecessary quotes will cause warnings. The following patterns are considered problems:

/*eslint quote-props: ["error", "as-needed"]*/

var object = {
    "a": 0,
    "0": 0,
    "true": 0,
    "null": 0
};

The following patterns are not considered problems:

/*eslint quote-props: ["error", "as-needed"]*/
/*eslint-env es6*/

var object1 = {
    "a-b": 0,
    "0x0": 0,
    "1e2": 0
};

var object2 = {
    foo: 'bar',
    baz: 42,
    true: 0,
    0: 0,
    'qux-lorem': true
};

var object3 = {
    foo() {
        return;
    }
};

When the "as-needed" mode is selected, an additional keywords option can be provided. This flag indicates whether language keywords should be quoted as properties. By default it is set to false.

{
    "quote-props": ["error", "as-needed", { "keywords": true }]
}

When keywords is set to true, the following patterns become problems:

/*eslint quote-props: ["error", "as-needed", { "keywords": true }]*/

var x = {
    while: 1,
    volatile: "foo"
};

Another modifier for this rule is the unnecessary option which defaults to true. Setting this to false will prevent the rule from complaining about unnecessarily quoted properties. This comes in handy when you only care about quoting keywords.

{
    "quote-props": ["error", "as-needed", { "keywords": true, "unnecessary": false }]
}

When unnecessary is set to false, the following patterns stop being problems:

/*eslint quote-props: ["error", "as-needed", { "keywords": true, "unnecessary": false }]*/

var x = {
    "while": 1,
    "foo": "bar"  // Would normally have caused a warning
};

A numbers flag, with default value false, can also be used as a modifier for the "as-needed" mode. When it is set to true, numeric literals should always be quoted.

{
    "quote-props": ["error", "as-needed", {"numbers": true}]
}

When numbers is set to true, the following patterns become problems:

/*eslint quote-props: ["error", "as-needed", { "numbers": true }]*/

var x = {
    100: 1
}

and the following patterns stop being problems:

var x = {
    "100": 1
}

"consistent"

When configured with "consistent", the patterns below are considered problems. Basically "consistent" means all or no properties are expected to be quoted, in other words quoting style can't be mixed within an object. Please note the latter situation (no quotation at all) isn't always possible as some property names require quoting.

/*eslint quote-props: ["error", "consistent"]*/

var object1 = {
    foo: "bar",
    "baz": 42,
    "qux-lorem": true
};

var object2 = {
    'foo': 'bar',
    baz: 42
};

The following patterns are not considered problems:

/*eslint quote-props: ["error", "consistent"]*/

var object1 = {
    "foo": "bar",
    "baz": 42,
    "qux-lorem": true
};

var object2 = {
    'foo': 'bar',
    'baz': 42
};

var object3 = {
    foo: 'bar',
    baz: 42
};

"consistent-as-needed"

When configured with "consistent-as-needed", the behavior is similar to "consistent" with one difference. Namely, properties' quoting should be consistent (as in "consistent") but whenever all quotes are redundant a warning is raised. In other words if at least one property name has to be quoted (like qux-lorem) then all property names must be quoted, otherwise no properties can be quoted. The following patterns are considered problems:

/*eslint quote-props: ["error", "consistent-as-needed"]*/

var object1 = {
    foo: "bar",
    "baz": 42,
    "qux-lorem": true
};

var object2 = {
    'foo': 'bar',
    'baz': 42
};

The following patterns are not considered problems:

/*eslint quote-props: ["error", "consistent-as-needed"]*/

var object1 = {
    "foo": "bar",
    "baz": 42,
    "qux-lorem": true
};

var object2 = {
    foo: 'bar',
    baz: 42
};

When the "consistent-as-needed" mode is selected, an additional keywords option can be provided. This flag indicates whether language keywords can be used unquoted as properties. By default it is set to false.

{
    "quote-props": ["error", "consistent-as-needed", { "keywords": true }]
}

When keywords is set to true, the following patterns are considered problems:

/*eslint quote-props: ["error", "consistent-as-needed", { "keywords": true }]*/

var x = {
    while: 1,
    volatile: "foo"
};

When Not To Use It

If you don't care if property names are consistently wrapped in quotes or not, and you don't target legacy ES3 environments, turn this rule off.

Further Reading

• Reserved words as property names
• Unquoted property names / object keys in JavaScript Source: http://eslint.org/docs/rules/

        })

Close

Enforce or Disallow Semicolons (semi)

(fixable) The --fix option on the [command line](../user-guide/command-line-interface#fix) automatically fixes problems reported by this rule.

JavaScript is unique amongst the C-like languages in that it doesn't require semicolons at the end of each statement. In many cases, the JavaScript engine can determine that a semicolon should be in a certain spot and will automatically add it. This feature is known as automatic semicolon insertion (ASI) and is considered one of the more controversial features of JavaScript. For example, the following lines are both valid:

var name = "ESLint"
var website = "eslint.org";

On the first line, the JavaScript engine will automatically insert a semicolon, so this is not considered a syntax error. The JavaScript engine still knows how to interpret the line and knows that the line end indicates the end of the statement.

In the debate over ASI, there are generally two schools of thought. The first is that we should treat ASI as if it didn't exist and always include semicolons manually. The rationale is that it's easier to always include semicolons than to try to remember when they are or are not required, and thus decreases the possibility of introducing an error.

However, the ASI mechanism can sometimes be tricky to people who are using semicolons. For example, consider this code:

return
{
    name: "ESLint"
};

This may look like a return statement that returns an object literal, however, the JavaScript engine will interpret this code as:

return;
{
    name: "ESLint";
}

Effectively, a semicolon is inserted after the return statement, causing the code below it (a labeled literal inside a block) to be unreachable. This rule and the [no-unreachable](no-unreachable.md) rule will protect your code from such cases.

On the other side of the argument are those who says that since semicolons are inserted automatically, they are optional and do not need to be inserted manually. However, the ASI mechanism can also be tricky to people who don't use semicolons. For example, consider this code:

var globalCounter = { }

(function () {
    var n = 0
    globalCounter.increment = function () {
        return ++n
    }
})()

In this example, a semicolon will not be inserted after the first line, causing a run-time error (because an empty object is called as if it's a function). The [no-unexpected-multiline](no-unexpected-multiline.md) rule can protect your code from such cases.

Although ASI allows for more freedom over your coding style, it can also make your code behave in an unexpected way, whether you use semicolons or not. Therefore, it is best to know when ASI takes place and when it does not, and have ESLint protect your code from these potentially unexpected cases. In short, as once described by Isaac Schlueter, a \n character always ends a statement (just like a semicolon) unless one of the following is true:

1. The statement has an unclosed paren, array literal, or object literal or ends in some other way that is not a valid way to end a statement. (For instance, ending with . or ,.)
2. The line is -- or ++ (in which case it will decrement/increment the next token.)
3. It is a for(), while(), do, if(), or else, and there is no {
4. The next line starts with [, (, +, *, /, -, ,, ., or some other binary operator that can only be found between two tokens in a single expression.

Rule Details

This rule is aimed at ensuring consistent use of semicolons. You can decide whether or not to require semicolons at the end of statements.

Options

The rule takes one or two options. The first one is a string, which could be "always" or "never". The default is "always". The second one is an object for more fine-grained configuration when the first option is "always".

You can set the option in configuration like this:

"always"

By using the default option, semicolons must be used any place where they are valid.

semi: ["error", "always"]

The following patterns are considered problems:

/*eslint semi: "error"*/

var name = "ESLint"

object.method = function() {
    // ...
}

The following patterns are not considered problems:

/*eslint semi: "error"*/

var name = "ESLint";

object.method = function() {
    // ...
};

Fine-grained control

When setting the first option as "always", an additional option can be added to omit the last semicolon in a one-line block, that is, a block in which its braces (and therefore the content of the block) are in the same line:

semi: ["error", "always", { "omitLastInOneLineBlock": true}]

The following patterns are considered problems:

/*eslint semi: ["error", "always", { "omitLastInOneLineBlock": true}] */

if (foo) {
    bar()
}

if (foo) { bar(); }

The following patterns are not considered problems:

/*eslint semi: ["error", "always", { "omitLastInOneLineBlock": true}] */

if (foo) { bar() }

if (foo) { bar(); baz() }

"never"

If you want to enforce that semicolons are never used, switch the configuration to:

semi: [2, "never"]

Then, the following patterns are considered problems:

/*eslint semi: ["error", "never"]*/

var name = "ESLint";

object.method = function() {
    // ...
};

And the following patterns are not considered problems:

/*eslint semi: ["error", "never"]*/

var name = "ESLint"

object.method = function() {
    // ...
}

Even in "never" mode, semicolons are still allowed to disambiguate statements beginning with [, (, /, +, or -:

/*eslint semi: ["error", "never"]*/

var name = "ESLint"

;(function() {
    // ...
})()

When Not To Use It

If you do not want to enforce semicolon usage (or omission) in any particular way, then you can turn this rule off.

Further Reading

• An Open Letter to JavaScript Leaders Regarding Semicolons
• JavaScript Semicolon Insertion
• Understanding Automatic Semicolon Insertion in JavaScript

Related Rules

• [no-extra-semi](no-extra-semi.md)
• [no-unexpected-multiline](no-unexpected-multiline.md)
• [semi-spacing](semi-spacing.md) Source: http://eslint.org/docs/rules/

        if (index == 0) {

Close

Require === and !== (eqeqeq)

It is considered good practice to use the type-safe equality operators === and !== instead of their regular counterparts == and !=.

The reason for this is that == and != do type coercion which follows the rather obscure Abstract Equality Comparison Algorithm. For instance, the following statements are all considered true:

• [] == false
• [] == ![]
• 3 == "03"

If one of those occurs in an innocent-looking statement such as a == b the actual problem is very difficult to spot.

Rule Details

This rule is aimed at eliminating the type-unsafe equality operators.

Examples of incorrect code for this rule:

/*eslint eqeqeq: "error"*/

if (x == 42) { }

if ("" == text) { }

if (obj.getStuff() != undefined) { }

Options

smart

The "smart" option enforces the use of === and !== except for these cases:

• Comparing two literal values
• Evaluating the value of typeof
• Comparing against null

Examples of incorrect code for the "smart" option:

/*eslint eqeqeq: ["error", "smart"]*/

// comparing two variables requires ===
a == b

// only one side is a literal
foo == true
bananas != 1

// comparing to undefined requires ===
value == undefined

Examples of correct code for the "smart" option:

/*eslint eqeqeq: ["error", "smart"]*/

typeof foo == 'undefined'
'hello' != 'world'
0 == 0
true == true
foo == null

allow-null

The "allow-null" option will enforce === and !== in your code with one exception - it permits comparing to null to check for null or undefined in a single expression.

Examples of incorrect code for the "allow-null" option:

/*eslint eqeqeq: ["error", "allow-null"]*/

bananas != 1
typeof foo == 'undefined'
'hello' != 'world'
0 == 0
foo == undefined

Examples of correct code for the "allow-null" option:

/*eslint eqeqeq: ["error", "allow-null"]*/

foo == null

When Not To Use It

If you don't want to enforce a style for using equality operators, then it's safe to disable this rule. Source: http://eslint.org/docs/rules/

  function mergeGrps(inputGrp1, inputGrp2) {

Close

Require JSDoc comment (require-jsdoc)

JSDoc is a JavaScript API documentation generator. It uses specially-formatted comments inside of code to generate API documentation automatically. For example, this is what a JSDoc comment looks like for a function:

/**
 * Adds two numbers together.
 * @param {int} num1 The first number.
 * @param {int} num2 The second number.
 * @returns {int} The sum of the two numbers.
 */
function sum(num1, num2) {
    return num1 + num2;
}

Some style guides require JSDoc comments for all functions as a way of explaining function behavior.

Rule Details

This rule generates warnings for nodes that do not have JSDoc comments when they should. Supported nodes:

• FunctionDeclaration
• ClassDeclaration
• MethodDefinition

Options

This rule accepts a require object with its properties as

• FunctionDeclaration (default: true)
• ClassDeclaration (default: false)
• MethodDefinition (default: false)

Default option settings are

{
    "require-jsdoc": ["error", {
        "require": {
            "FunctionDeclaration": true,
            "MethodDefinition": false,
            "ClassDeclaration": false
        }
    }]
}

The following patterns are considered problems:

/*eslint "require-jsdoc": ["error", {
    "require": {
        "FunctionDeclaration": true,
        "MethodDefinition": true,
        "ClassDeclaration": true
    }
}]*/

function foo() {
    return 10;
}

class Test{
    getDate(){}
}

The following patterns are not considered problems:

/*eslint "require-jsdoc": ["error", {
    "require": {
        "FunctionDeclaration": true,
        "MethodDefinition": true,
        "ClassDeclaration": true
    }
}]*/

/**
* It returns 10
*/
function foo() {
    return 10;
}

/**
* It returns 10
*/
var foo = function() {
    return 10;
}

var array = [1,2,3];
array.filter(function(item) {
    return item > 2;
});

/**
* It returns 10
*/
class Test{
    /**
    * returns the date
    */
    getDate(){}
}

When Not To Use It

If you do not require JSDoc for your functions, then you can leave this rule off.

Related Rules

• [valid-jsdoc](valid-jsdoc.md) Source: http://eslint.org/docs/rules/

    function initCanvasDownloadData() {

Close

Require JSDoc comment (require-jsdoc)

JSDoc is a JavaScript API documentation generator. It uses specially-formatted comments inside of code to generate API documentation automatically. For example, this is what a JSDoc comment looks like for a function:

/**
 * Adds two numbers together.
 * @param {int} num1 The first number.
 * @param {int} num2 The second number.
 * @returns {int} The sum of the two numbers.
 */
function sum(num1, num2) {
    return num1 + num2;
}

Some style guides require JSDoc comments for all functions as a way of explaining function behavior.

Rule Details

This rule generates warnings for nodes that do not have JSDoc comments when they should. Supported nodes:

• FunctionDeclaration
• ClassDeclaration
• MethodDefinition

Options

This rule accepts a require object with its properties as

• FunctionDeclaration (default: true)
• ClassDeclaration (default: false)
• MethodDefinition (default: false)

Default option settings are

{
    "require-jsdoc": ["error", {
        "require": {
            "FunctionDeclaration": true,
            "MethodDefinition": false,
            "ClassDeclaration": false
        }
    }]
}

The following patterns are considered problems:

/*eslint "require-jsdoc": ["error", {
    "require": {
        "FunctionDeclaration": true,
        "MethodDefinition": true,
        "ClassDeclaration": true
    }
}]*/

function foo() {
    return 10;
}

class Test{
    getDate(){}
}

The following patterns are not considered problems:

/*eslint "require-jsdoc": ["error", {
    "require": {
        "FunctionDeclaration": true,
        "MethodDefinition": true,
        "ClassDeclaration": true
    }
}]*/

/**
* It returns 10
*/
function foo() {
    return 10;
}

/**
* It returns 10
*/
var foo = function() {
    return 10;
}

var array = [1,2,3];
array.filter(function(item) {
    return item > 2;
});

/**
* It returns 10
*/
class Test{
    /**
    * returns the date
    */
    getDate(){}
}

When Not To Use It

If you do not require JSDoc for your functions, then you can leave this rule off.

Related Rules

• [valid-jsdoc](valid-jsdoc.md) Source: http://eslint.org/docs/rules/

    ':groupid="attributes.group_id" :reset-btn-id="resetBtnId" :chart-ctrl="chartInst" ' +

Close

enforce a maximum line length (max-len)

Very long lines of code in any language can be difficult to read. In order to aid in readability and maintainability many coders have developed a convention to limit lines of code to X number of characters (traditionally 80 characters).

var foo = { "bar": "This is a bar.", "baz": { "qux": "This is a qux" }, "difficult": "to read" }; // very long

Rule Details

This rule enforces a maximum line length to increase code readability and maintainability.

Note: This rule calculates the length of a line via code points, not characters. That means if you use a double-byte character in your code, it will count as 2 code points instead of 1, and 2 will be used to calculate line length. This is a technical limitation of JavaScript that is made easier with ES2015, and we will look to update this when ES2015 is available in Node.js.

Options

This rule has a number or object option:

• "code" (default 80) enforces a maximum line length
• "tabWidth" (default 4) specifies the character width for tab characters
• "comments" enforces a maximum line length for comments; defaults to value of code
• "ignorePattern" ignores lines matching a regular expression; can only match a single line and need to be double escaped when written in YAML or JSON
• "ignoreComments": true ignores all trailing comments and comments on their own line
• "ignoreTrailingComments": true ignores only trailing comments
• "ignoreUrls": true ignores lines that contain a URL

code

Examples of incorrect code for this rule with the default { "code": 80 } option:

/*eslint max-len: ["error", 80]*/

var foo = { "bar": "This is a bar.", "baz": { "qux": "This is a qux" }, "difficult": "to read" };

Examples of correct code for this rule with the default { "code": 80 } option:

/*eslint max-len: ["error", 80]*/

var foo = {
  "bar": "This is a bar.",
  "baz": { "qux": "This is a qux" },
  "easier": "to read"
};

tabWidth

Examples of incorrect code for this rule with the default { "tabWidth": 4 } option:

/*eslint max-len: ["error", 80, 4]*/

\t  \t  var foo = { "bar": "This is a bar.", "baz": { "qux": "This is a qux" } };

Examples of correct code for this rule with the default { "tabWidth": 4 } option:

/*eslint max-len: ["error", 80, 4]*/

\t  \t  var foo = {
\t  \t  \t  \t  "bar": "This is a bar.",
\t  \t  \t  \t  "baz": { "qux": "This is a qux" }
\t  \t  };

comments

Examples of incorrect code for this rule with the { "comments": 65 } option:

/*eslint max-len: ["error", { "comments": 65 }]*/

/**
 * This is a comment that violates the maximum line length we have specified
**/

ignoreComments

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

/*eslint max-len: ["error", { "ignoreComments": true }]*/

/**
 * This is a really really really really really really really really really long comment
**/

ignoreTrailingComments

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

/*eslint max-len: ["error", { "ignoreTrailingComments": true }]*/

var foo = 'bar'; // This is a really really really really really really really long comment

ignoreUrls

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

/*eslint max-len: ["error", { "ignoreUrls": true }]*/

var url = 'https://www.example.com/really/really/really/really/really/really/really/long';

ignorePattern

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

/*eslint max-len: ["error", { "ignorePattern": "^\\s*var\\s.+=\\s*require\\s*\\(/" }]*/

var dep = require('really/really/really/really/really/really/really/really/long/module');

Related Rules

• [complexity](complexity.md)
• [max-depth](max-depth.md)
• [max-nested-callbacks](max-nested-callbacks.md)
• [max-params](max-params.md)
• [max-statements](max-statements.md) Source: http://eslint.org/docs/rules/

                  tooltip.find('.cohort-name').val() : tooltip.find('.cohort-name').attr('placeholder');

Close

enforce a maximum line length (max-len)

Very long lines of code in any language can be difficult to read. In order to aid in readability and maintainability many coders have developed a convention to limit lines of code to X number of characters (traditionally 80 characters).

var foo = { "bar": "This is a bar.", "baz": { "qux": "This is a qux" }, "difficult": "to read" }; // very long

Rule Details

This rule enforces a maximum line length to increase code readability and maintainability.

Note: This rule calculates the length of a line via code points, not characters. That means if you use a double-byte character in your code, it will count as 2 code points instead of 1, and 2 will be used to calculate line length. This is a technical limitation of JavaScript that is made easier with ES2015, and we will look to update this when ES2015 is available in Node.js.

Options

This rule has a number or object option:

• "code" (default 80) enforces a maximum line length
• "tabWidth" (default 4) specifies the character width for tab characters
• "comments" enforces a maximum line length for comments; defaults to value of code
• "ignorePattern" ignores lines matching a regular expression; can only match a single line and need to be double escaped when written in YAML or JSON
• "ignoreComments": true ignores all trailing comments and comments on their own line
• "ignoreTrailingComments": true ignores only trailing comments
• "ignoreUrls": true ignores lines that contain a URL

code

Examples of incorrect code for this rule with the default { "code": 80 } option:

/*eslint max-len: ["error", 80]*/

var foo = { "bar": "This is a bar.", "baz": { "qux": "This is a qux" }, "difficult": "to read" };

Examples of correct code for this rule with the default { "code": 80 } option:

/*eslint max-len: ["error", 80]*/

var foo = {
  "bar": "This is a bar.",
  "baz": { "qux": "This is a qux" },
  "easier": "to read"
};

tabWidth

Examples of incorrect code for this rule with the default { "tabWidth": 4 } option:

/*eslint max-len: ["error", 80, 4]*/

\t  \t  var foo = { "bar": "This is a bar.", "baz": { "qux": "This is a qux" } };

Examples of correct code for this rule with the default { "tabWidth": 4 } option:

/*eslint max-len: ["error", 80, 4]*/

\t  \t  var foo = {
\t  \t  \t  \t  "bar": "This is a bar.",
\t  \t  \t  \t  "baz": { "qux": "This is a qux" }
\t  \t  };

comments

Examples of incorrect code for this rule with the { "comments": 65 } option:

/*eslint max-len: ["error", { "comments": 65 }]*/

/**
 * This is a comment that violates the maximum line length we have specified
**/

ignoreComments

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

/*eslint max-len: ["error", { "ignoreComments": true }]*/

/**
 * This is a really really really really really really really really really long comment
**/

ignoreTrailingComments

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

/*eslint max-len: ["error", { "ignoreTrailingComments": true }]*/

var foo = 'bar'; // This is a really really really really really really really long comment

ignoreUrls

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

/*eslint max-len: ["error", { "ignoreUrls": true }]*/

var url = 'https://www.example.com/really/really/really/really/really/really/really/long';

ignorePattern

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

/*eslint max-len: ["error", { "ignorePattern": "^\\s*var\\s.+=\\s*require\\s*\\(/" }]*/

var dep = require('really/really/really/really/really/really/really/really/long/module');

Related Rules

• [complexity](complexity.md)
• [max-depth](max-depth.md)
• [max-nested-callbacks](max-nested-callbacks.md)
• [max-params](max-params.md)
• [max-statements](max-statements.md) Source: http://eslint.org/docs/rules/