disallow unnecessary parentheses (no-extra-parens)

禁止冗余的括号（no-extra-parens）

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

命令行中的 --fix 选项可以自动修复一些该规则报告的问题。

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

该规则对圆括号的使用做了限制，只有在必要的地方才能使用。

Rule Details

This rule always ignores extra parentheses around the following:

该规则总是忽略以下情况的额外的圆括号：

• RegExp literals such as (/abc/).test(var) to avoid conflicts with the wrap-regex rule
• RegExp 字面量比如 (/abc/).test(var) 避免与 wrap-regex 规则产生冲突
• 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
• 立即执行函数 (也就是 IIFE) 比如 var x = (function () {})(); 和 ((function foo() {return 1;})()) 避免与 wrap-iife 规则产生冲突
• arrow function arguments to avoid conflicts with the arrow-parens rule
• 箭头函数参数避免与 arrow-parens 规则产生冲突

Options

This rule has a string option:

该规则有一个字符串选项：

• "all" (default) disallows unnecessary parentheses around any expression
• "all" (默认) 禁止在 任何 表达式周围出现不必要的圆括号
• "functions" disallows unnecessary parentheses only around function expressions
• "functions" 只在 函数表达式周围禁止不必要的圆括号

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

该规则对于 "all" 选项有例外情况，是个对象：

• "conditionalAssign": false allows extra parentheses around assignments in conditional test expressions
• "conditionalAssign": false 允许在条件语句的测试表达式中的赋值语句周围出现额外的圆括号
• "returnAssign": false allows extra parentheses around assignments in return statements
• "returnAssign": false 允许在 return 语句中的赋值语句周围出现额外的圆括号
• "nestedBinaryExpressions": false allows extra parentheses in nested binary expressions
• "nestedBinaryExpressions": false 允许在嵌套的二元表达式中出现额外的圆括号
• "ignoreJSX": "none|all|multi-line|single-line" allows extra parentheses around no/all/multi-line/single-line JSX components. Defaults to none.
• "ignoreJSX": "none|all|multi-line|single-line" 允许在 no/所有/多行/单行的JSX 组件周围出现额外的圆括号。 默认为 none。
• "enforceForArrowConditionals": false allows extra parentheses around ternary expressions which are the body of an arrow function
• "enforceForArrowConditionals": false 允许在箭头函数体中的三元表达式周围出现额外的圆括号

all

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

默认选项 "all" 的 错误 代码示例：

/* 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:

默认选项 "all" 的 正确 代码示例：

/* 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:

选项 "all" 和 { "conditionalAssign": false } 的 正确 代码示例：

/* 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:

选项 "all" 和 { "returnAssign": false } 的 正确 代码示例：

/* 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:

选项 "all" 和 { "nestedBinaryExpressions": false } 的 正确 代码示例：

/* 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:

选项 all 和 { "ignoreJSX": "all" } 正确 代码示例：

/* 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:

选项 all 和 { "ignoreJSX": "multi-line" } 的 错误 代码示例：

/* 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:

选项 all 和 { "ignoreJSX": "multi-line" } 的 正确 代码示例：

/* 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:

选项 all 和 { "ignoreJSX": "single-line" } 的 错误 代码示例：

/* 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:

选项 all 和 { "ignoreJSX": "single-line" } 的 正确 代码示例：

/* 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:

选项 "all" and { "enforceForArrowConditionals": false } 的 正确 代码示例：

/* 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:

选项 "functions" 的 错误 代码示例：

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

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

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

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

选项 "functions" 的 正确 代码示例：

/* 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

• MDN: Operator Precedence

Related Rules

• arrow-parens
• no-cond-assign
• no-return-assign

Version

This rule was introduced in ESLint 0.1.4.

该规则在 ESLint 0.1.4 中被引入。

Resources

• Rule source
• Documentation source