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:
- 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
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 inreturn
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 tonone
.
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>)
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
Version
This rule was introduced in ESLint 0.1.4.