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disallow unnecessary parentheses (no-extra-parens)

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

Rule Details

This rule always ignores extra parentheses around the following:

  • RegExp literals such as (/abc/).test(var) to avoid conflicts with the wrap-regex rule
  • immediately-invoked function expressions (also known as IIFEs) such as var x = (function () {})(); and ((function foo() {return 1;})()) to avoid conflicts with the wrap-iife rule
  • arrow function arguments to avoid conflicts with the arrow-parens rule

Options

This rule has a string option:

  • "all" (default) disallows unnecessary parentheses around any expression
  • "functions" disallows unnecessary parentheses only around function expressions

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

  • "conditionalAssign": false allows extra parentheses around assignments in conditional test expressions
  • "returnAssign": false allows extra parentheses around assignments in return statements
  • "nestedBinaryExpressions": false allows extra parentheses in nested binary expressions
  • "ignoreJSX": "none|all|multi-line|single-line" allows extra parentheses around no/all/multi-line/single-line JSX components. Defaults to none.
  • "enforceForArrowConditionals": false allows extra parentheses around ternary expressions which are the body of an arrow function
  • "enforceForSequenceExpressions": false allows extra parentheses around sequence expressions
  • "enforceForNewInMemberExpressions": false allows extra parentheses around new expressions in member expressions

all

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

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

a = (b * c);

(a * b) + c;

for (a in (b, c));

for (a in (b));

for (a of (b));

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);

for (a of (b, c));

for (a of b);

for (a in b, c);

for (a in b);

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);

enforceForSequenceExpressions

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

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

(a, b);

if ((val = foo(), val < 10)) {}

while ((val = foo(), val < 10));

enforceForNewInMemberExpressions

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

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

const foo = (new Bar()).baz;

const quux = (new Bar())[baz];

(new Bar()).doSomething();

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

Related Rules