eqeqeq

要求使用 === 和 !==

使用类型安全的相等运算符 === 和 !== 而不是它们的常规对应项 == 和 != 被认为是一种很好的做法。

¥It is considered good practice to use the type-safe equality operators === and !== instead of their regular counterparts == and !=.

原因是 == 和 != 在相当晦涩的 抽象等式比较算法 之后进行类型强制。例如，以下语句都被视为 true：

¥The reason for this is that == and != do type coercion which follows the rather obscure Abstract Equality Comparison Algorithm. For instance, the following statements are all considered true:

• [] == false

• [] == ![]

• 3 == "03"

如果其中一个出现在诸如 a == b 之类的看似无辜的声明中，则很难发现实际问题。

¥If one of those occurs in an innocent-looking statement such as a == b the actual problem is very difficult to spot.

规则详情

¥Rule Details

此规则旨在消除类型不安全的相等运算符。

¥This rule is aimed at eliminating the type-unsafe equality operators.

此规则的错误代码示例：

¥Examples of incorrect code for this rule:

/*eslint eqeqeq: "error"*/

if (x == 42) { }

if ("" == text) { }

if (obj.getStuff() != undefined) { }
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命令行中的 --fix 选项会自动修复此规则报告的一些问题。只有当其中一个操作数是 typeof 表达式，或者两个操作数都是具有相同类型的字面时，才会解决问题。

¥The --fix option on the command line automatically fixes some problems reported by this rule. A problem is only fixed if one of the operands is a typeof expression, or if both operands are literals with the same type.

选项

¥Options

always

"always" 选项（默认）强制在每种情况下使用 === 和 !==（除非你选择更具体地处理 null [见下文]）。

¥The "always" option (default) enforces the use of === and !== in every situation (except when you opt-in to more specific handling of null [see below]).

"always" 选项的错误代码示例：

¥Examples of incorrect code for the "always" option:

/*eslint eqeqeq: ["error", "always"]*/

a == b
foo == true
bananas != 1
value == undefined
typeof foo == 'undefined'
'hello' != 'world'
0 == 0
true == true
foo == null

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"always" 选项的正确代码示例：

¥Examples of correct code for the "always" option:

/*eslint eqeqeq: ["error", "always"]*/

a === b
foo === true
bananas !== 1
value === undefined
typeof foo === 'undefined'
'hello' !== 'world'
0 === 0
true === true
foo === null

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此规则可选地采用第二个参数，它应该是具有以下受支持属性的对象：

¥This rule optionally takes a second argument, which should be an object with the following supported properties:

• "null"：自定义此规则如何处理 null 字面。可能的值：

  ¥"null": Customize how this rule treats null literals. Possible values:

  • always（默认） - 始终使用 === 或 !==。

    ¥always (default) - Always use === or !==.

  • never - 切勿将 === 或 !== 与 null 一起使用。

    ¥never - Never use === or !== with null.

  • ignore - 不要将此规则应用于 null。

    ¥ignore - Do not apply this rule to null.

smart

"smart" 选项强制使用 === 和 !==，但以下情况除外：

¥The "smart" option enforces the use of === and !== except for these cases:

• 比较两个字面量值。

  ¥Comparing two literal values.

• 评估 typeof 的值。

  ¥Evaluating the value of typeof.

• 与 null 进行比较。

  ¥Comparing against null.

"smart" 选项的错误代码示例：

¥Examples of incorrect code for the "smart" option:

/*eslint eqeqeq: ["error", "smart"]*/

// comparing two variables requires ===
a == b

// only one side is a literal
foo == true
bananas != 1

// comparing to undefined requires ===
value == undefined
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"smart" 选项的正确代码示例：

¥Examples of correct code for the "smart" option:

/*eslint eqeqeq: ["error", "smart"]*/

typeof foo == 'undefined'
'hello' != 'world'
0 == 0
true == true
foo == null
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allow-null

已弃用：不要使用此选项，而是使用 "always" 并传递值为 "ignore" 的 "null" 选项属性。这将告诉 ESLint 始终强制执行严格相等，除非与 null 字面进行比较。

¥Deprecated: Instead of using this option use "always" and pass a "null" option property with value "ignore". This will tell ESLint to always enforce strict equality except when comparing with the null literal.

["error", "always", {"null": "ignore"}]
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何时不使用

¥When Not To Use It

如果你不想强制使用相等运算符的样式，那么禁用此规则是安全的。

¥If you don’t want to enforce a style for using equality operators, then it’s safe to disable this rule.

版本

此规则是在 ESLint v0.0.2 中引入。

资源

• 规则源码
• 测试源码