disallow unnecessary parentheses (no-extra-parens)

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

This rule restricts the use of parentheses to only where they are necessary.

Rule Details

This rule always ignores extra parentheses around the following:

Options

This rule has a string option:

This rule has an object option for exceptions to the "all" option:

all

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

/* eslint no-extra-parens: "error" */

a = (b * c);

(a * b) + c;

typeof (a);

(function(){} ? a() : b());

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

/* eslint no-extra-parens: "error" */

(0).toString();

(Object.prototype.toString.call());

({}.toString.call());

(function(){}) ? a() : b();

(/^a$/).test(x);

conditionalAssign

Examples of correct code for this rule with the "all" and { "conditionalAssign": false } options:

/* eslint no-extra-parens: ["error", "all", { "conditionalAssign": false }] */

while ((foo = bar())) {}

if ((foo = bar())) {}

do; while ((foo = bar()))

for (;(a = b););

returnAssign

Examples of correct code for this rule with the "all" and { "returnAssign": false } options:

/* eslint no-extra-parens: ["error", "all", { "returnAssign": false }] */

function a(b) {
  return (b = 1);
}

function a(b) {
  return b ? (c = d) : (c = e);
}

b => (b = 1);

b => b ? (c = d) : (c = e);

nestedBinaryExpressions

Examples of correct code for this rule with the "all" and { "nestedBinaryExpressions": false } options:

/* eslint no-extra-parens: ["error", "all", { "nestedBinaryExpressions": false }] */

x = a || (b && c);
x = a + (b * c);
x = (a * b) / c;

ignoreJSX

Examples of correct code for this rule with the all and { "ignoreJSX": "all" } options:

/* eslint no-extra-parens: ["error", "all", { ignoreJSX: "all" }] */
const Component = (<div />)
const Component = (
    <div
        prop={true}
    />
)

Examples of incorrect code for this rule with the all and { "ignoreJSX": "multi-line" } options:

/* eslint no-extra-parens: ["error", "all", { ignoreJSX: "multi-line" }] */
const Component = (<div />)
const Component = (<div><p /></div>)

Examples of correct code for this rule with the all and { "ignoreJSX": "multi-line" } options:

/* eslint no-extra-parens: ["error", "all", { ignoreJSX: "multi-line" }] */
const Component = (
    <div>
        <p />
    </div>
)
const Component = (
    <div
        prop={true}
    />
)

Examples of incorrect code for this rule with the all and { "ignoreJSX": "single-line" } options:

/* eslint no-extra-parens: ["error", "all", { ignoreJSX: "single-line" }] */
const Component = (
    <div>
        <p />
    </div>
)
const Component = (
    <div
        prop={true}
    />
)

Examples of correct code for this rule with the all and { "ignoreJSX": "single-line" } options:

/* eslint no-extra-parens: ["error", "all", { ignoreJSX: "single-line" }] */
const Component = (<div />)
const Component = (<div><p /></div>)

enforceForArrowConditionals

Examples of correct code for this rule with the "all" and { "enforceForArrowConditionals": false } options:

/* eslint no-extra-parens: ["error", "all", { "enforceForArrowConditionals": false }] */

const b = a => 1 ? 2 : 3;
const d = c => (1 ? 2 : 3);

functions

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

/* eslint no-extra-parens: ["error", "functions"] */

((function foo() {}))();

var y = (function () {return 1;});

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

/* eslint no-extra-parens: ["error", "functions"] */

(0).toString();

(Object.prototype.toString.call());

({}.toString.call());

(function(){} ? a() : b());

(/^a$/).test(x);

a = (b * c);

(a * b) + c;

typeof (a);

Further Reading

Version

This rule was introduced in ESLint 0.1.4.

Resources