use-isnan

检查 NaN 时需要调用 isNaN()

在 JavaScript 中，NaN 是 Number 类型的一个特殊值。它用于表示由 IEEE 二进制浮点算术标准指定的双精度 64 位格式表示的任何 “not-a-number” 值。

¥In JavaScript, NaN is a special value of the Number type. It’s used to represent any of the “not-a-number” values represented by the double-precision 64-bit format as specified by the IEEE Standard for Binary Floating-Point Arithmetic.

因为 NaN 在 JavaScript 中是独一无二的，它不等于任何东西，包括它自己，所以与 NaN 的比较结果令人困惑：

¥Because NaN is unique in JavaScript by not being equal to anything, including itself, the results of comparisons to NaN are confusing:

• NaN === NaN 或 NaN == NaN 评估为假

  ¥NaN === NaN or NaN == NaN evaluate to false

• NaN !== NaN 或 NaN != NaN 评估为真

  ¥NaN !== NaN or NaN != NaN evaluate to true

因此，使用 Number.isNaN() 或全局 isNaN() 函数来测试一个值是否为 NaN。

¥Therefore, use Number.isNaN() or global isNaN() functions to test whether a value is NaN.

规则详情

¥Rule Details

此规则不允许与 ‘NaN’ 进行比较。

¥This rule disallows comparisons to ‘NaN’.

此规则的错误代码示例：

¥Examples of incorrect code for this rule:

/*eslint use-isnan: "error"*/

if (foo == NaN) {
    // ...
}

if (foo != NaN) {
    // ...
}

if (foo == Number.NaN) {
    // ...
}

if (foo != Number.NaN) {
    // ...
}
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此规则的正确代码示例：

¥Examples of correct code for this rule:

/*eslint use-isnan: "error"*/

if (isNaN(foo)) {
    // ...
}

if (!isNaN(foo)) {
    // ...
}
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选项

¥Options

此规则有一个对象选项，有两个选项：

¥This rule has an object option, with two options:

• "enforceForSwitchCase": true（默认）另外不允许在 switch 语句中使用 case NaN 和 switch(NaN)。

  ¥"enforceForSwitchCase": true (default) additionally disallows case NaN and switch(NaN) in switch statements.

• "enforceForIndexOf": true 另外不允许将 indexOf 和 lastIndexOf 方法与 NaN 一起使用。默认为 false，这意味着默认情况下此规则不会警告 indexOf(NaN) 或 lastIndexOf(NaN) 方法调用。

  ¥"enforceForIndexOf": true additionally disallows the use of indexOf and lastIndexOf methods with NaN. Default is false, meaning that this rule by default does not warn about indexOf(NaN) or lastIndexOf(NaN) method calls.

enforceForSwitchCase

switch 语句在内部使用 === 比较来将表达式的值与 case 子句相匹配。因此，它永远无法匹配 case NaN。此外，switch(NaN) 永远不能匹配 case 子句。

¥The switch statement internally uses the === comparison to match the expression’s value to a case clause. Therefore, it can never match case NaN. Also, switch(NaN) can never match a case clause.

此规则的错误代码示例（"enforceForSwitchCase" 选项设置为 true（默认））：

¥Examples of incorrect code for this rule with "enforceForSwitchCase" option set to true (default):

/*eslint use-isnan: ["error", {"enforceForSwitchCase": true}]*/

switch (foo) {
    case NaN:
        bar();
        break;
    case 1:
        baz();
        break;
    // ...
}

switch (NaN) {
    case a:
        bar();
        break;
    case b:
        baz();
        break;
    // ...
}

switch (foo) {
    case Number.NaN:
        bar();
        break;
    case 1:
        baz();
        break;
    // ...
}

switch (Number.NaN) {
    case a:
        bar();
        break;
    case b:
        baz();
        break;
    // ...
}
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此规则的正确代码示例，其中 "enforceForSwitchCase" 选项设置为 true（默认）：

¥Examples of correct code for this rule with "enforceForSwitchCase" option set to true (default):

/*eslint use-isnan: ["error", {"enforceForSwitchCase": true}]*/

if (Number.isNaN(foo)) {
    bar();
} else {
    switch (foo) {
        case 1:
            baz();
            break;
        // ...
    }
}

if (Number.isNaN(a)) {
    bar();
} else if (Number.isNaN(b)) {
    baz();
} // ...
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此规则的正确代码示例（"enforceForSwitchCase" 选项设置为 false）：

¥Examples of correct code for this rule with "enforceForSwitchCase" option set to false:

/*eslint use-isnan: ["error", {"enforceForSwitchCase": false}]*/

switch (foo) {
    case NaN:
        bar();
        break;
    case 1:
        baz();
        break;
    // ...
}

switch (NaN) {
    case a:
        bar();
        break;
    case b:
        baz();
        break;
    // ...
}

switch (foo) {
    case Number.NaN:
        bar();
        break;
    case 1:
        baz();
        break;
    // ...
}

switch (Number.NaN) {
    case a:
        bar();
        break;
    case b:
        baz();
        break;
    // ...
}
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enforceForIndexOf

以下方法在内部使用 === 比较来将给定值与数组元素匹配：

¥The following methods internally use the === comparison to match the given value with an array element:

• Array.prototype.indexOf

• Array.prototype.lastIndexOf

因此，对于任何数组 foo，foo.indexOf(NaN) 和 foo.lastIndexOf(NaN) 将始终返回 -1。

¥Therefore, for any array foo, foo.indexOf(NaN) and foo.lastIndexOf(NaN) will always return -1.

如果你希望此规则报告 indexOf(NaN) 和 lastIndexOf(NaN) 方法调用，请将 "enforceForIndexOf" 设置为 true。

¥Set "enforceForIndexOf" to true if you want this rule to report indexOf(NaN) and lastIndexOf(NaN) method calls.

此规则的错误代码示例（"enforceForIndexOf" 选项设置为 true）：

¥Examples of incorrect code for this rule with "enforceForIndexOf" option set to true:

/*eslint use-isnan: ["error", {"enforceForIndexOf": true}]*/

var hasNaN = myArray.indexOf(NaN) >= 0;

var firstIndex = myArray.indexOf(NaN);

var lastIndex = myArray.lastIndexOf(NaN);

var indexWithSequenceExpression = myArray.indexOf((doStuff(), NaN));

var firstIndexFromSecondElement = myArray.indexOf(NaN, 1);

var lastIndexFromSecondElement = myArray.lastIndexOf(NaN, 1);
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此规则的正确代码示例（"enforceForIndexOf" 选项设置为 true）：

¥Examples of correct code for this rule with "enforceForIndexOf" option set to true:

/*eslint use-isnan: ["error", {"enforceForIndexOf": true}]*/

function myIsNaN(val) {
    return typeof val === "number" && isNaN(val);
}

function indexOfNaN(arr) {
    for (var i = 0; i < arr.length; i++) {
        if (myIsNaN(arr[i])) {
            return i;
        }
    }
    return -1;
}

function lastIndexOfNaN(arr) {
    for (var i = arr.length - 1; i >= 0; i--) {
        if (myIsNaN(arr[i])) {
            return i;
        }
    }
    return -1;
}

var hasNaN = myArray.some(myIsNaN);

var hasNaN = indexOfNaN(myArray) >= 0;

var firstIndex = indexOfNaN(myArray);

var lastIndex = lastIndexOfNaN(myArray);

// ES2015
var hasNaN = myArray.some(Number.isNaN);

// ES2015
var firstIndex = myArray.findIndex(Number.isNaN);

// ES2016
var hasNaN = myArray.includes(NaN);
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已知限制

¥Known Limitations

此选项检查具有给定名称的方法，即使具有该方法的对象不是数组。

¥This option checks methods with the given names, even if the object which has the method is not an array.

版本

此规则是在 ESLint v0.0.6 中引入。

资源

• 规则源码
• 测试源码