enforce consistent line breaks inside function parentheses (function-paren-newline)

The --fix option on the command line can automatically fix some of the problems reported by this rule.

Many style guides require or disallow newlines inside of function parentheses.

Rule Details

This rule enforces consistent line breaks inside parentheses of function parameters or arguments.

Options

This rule has a single option, which can either be a string or an object.

• "always" requires line breaks inside all function parentheses.
• "never" disallows line breaks inside all function parentheses.
• "multiline" (default) requires linebreaks inside function parentheses if any of the parameters/arguments have a line break between them. Otherwise, it disallows linebreaks.
• "multiline-arguments" works like multiline but allows linebreaks inside function parentheses if there is only one parameter/argument.
• "consistent" requires consistent usage of linebreaks for each pair of parentheses. It reports an error if one parenthesis in the pair has a linebreak inside it and the other parenthesis does not.
• { "minItems": value } requires linebreaks inside function parentheses if the number of parameters/arguments is at least value. Otherwise, it disallows linebreaks.

Example configurations:

{
  "rules": {
    "function-paren-newline": ["error", "never"]
  }
}

{
  "rules": {
    "function-paren-newline": ["error", { "minItems": 3 }]
  }
}

Examples of incorrect code for this rule with the "always" option:

/* eslint function-paren-newline: ["error", "always"] */

function foo(bar, baz) {}

var foo = function(bar, baz) {};

var foo = (bar, baz) => {};

foo(bar, baz);

Examples of correct code for this rule with the "always" option:

/* eslint function-paren-newline: ["error", "always"] */

function foo(
  bar,
  baz
) {}

var foo = function(
  bar, baz
) {};

var foo = (
  bar,
  baz
) => {};

foo(
  bar,
  baz
);

Examples of incorrect code for this rule with the "never" option:

/* eslint function-paren-newline: ["error", "never"] */

function foo(
  bar,
  baz
) {}

var foo = function(
  bar, baz
) {};

var foo = (
  bar,
  baz
) => {};

foo(
  bar,
  baz
);

Examples of correct code for this rule with the "never" option:

/* eslint function-paren-newline: ["error", "never"] */

function foo(bar, baz) {}

function foo(bar,
             baz) {}

var foo = function(bar, baz) {};

var foo = (bar, baz) => {};

foo(bar, baz);

foo(bar,
  baz);

Examples of incorrect code for this rule with the default "multiline" option:

/* eslint function-paren-newline: ["error", "multiline"] */

function foo(bar,
  baz
) {}

var foo = function(
  bar, baz
) {};

var foo = (
  bar,
  baz) => {};

foo(bar,
  baz);

foo(
  function() {
    return baz;
  }
);

Examples of correct code for this rule with the default "multiline" option:

/* eslint function-paren-newline: ["error", "multiline"] */

function foo(bar, baz) {}

var foo = function(
  bar,
  baz
) {};

var foo = (bar, baz) => {};

foo(bar, baz, qux);

foo(
  bar,
  baz,
  qux
);

foo(function() {
  return baz;
});

Examples of incorrect code for this rule with the "consistent" option:

/* eslint function-paren-newline: ["error", "consistent"] */

function foo(bar,
  baz
) {}

var foo = function(bar,
  baz
) {};

var foo = (
  bar,
  baz) => {};

foo(
  bar,
  baz);

foo(
  function() {
    return baz;
  });

Examples of correct code for this rule with the "consistent" option:

/* eslint function-paren-newline: ["error", "consistent"] */

function foo(bar,
  baz) {}

var foo = function(bar, baz) {};

var foo = (
  bar,
  baz
) => {};

foo(
  bar, baz
);

foo(
  function() {
    return baz;
  }
);

Examples of incorrect code for this rule with the "multiline-arguments" option:

/* eslint function-paren-newline: ["error", "multiline-arguments"] */

function foo(bar,
  baz
) {}

var foo = function(bar,
  baz
) {};

var foo = (
  bar,
  baz) => {};

foo(
  bar,
  baz);

foo(
  bar, qux,
  baz
);

Examples of correct code for this rule with the consistent "multiline-arguments" option:

/* eslint function-paren-newline: ["error", "multiline-arguments"] */

function foo(
  bar,
  baz
) {}

var foo = function(bar, baz) {};

var foo = (
  bar
) => {};

foo(
  function() {
    return baz;
  }
);

Examples of incorrect code for this rule with the { "minItems": 3 } option:

/* eslint function-paren-newline: ["error", { "minItems": 3 }] */

function foo(
  bar,
  baz
) {}

function foo(bar, baz, qux) {}

var foo = function(
  bar, baz
) {};

var foo = (bar,
  baz) => {};

foo(bar,
  baz);

Examples of correct code for this rule with the { "minItems": 3 } option:

/* eslint function-paren-newline: ["error", { "minItems": 3 }] */

function foo(bar, baz) {}

var foo = function(
  bar,
  baz,
  qux
) {};

var foo = (
  bar, baz, qux
) => {};

foo(bar, baz);

foo(
  bar, baz, qux
);

When Not To Use It

If don't want to enforce consistent linebreaks inside function parentheses, do not turn on this rule.

Version

This rule was introduced in ESLint 4.6.0.

Resources

• Rule source
• Documentation source