Number.isNaN()

¥Syntax

Number.isNaN(value)

¥Parameters

value

要测试 NaN 的值。

¥Return value

如果给定值是值为 NaN 的数字，则为布尔值 true。否则，false。

¥The boolean value true if the given value is a number with value NaN. Otherwise, false.

¥Description

函数 Number.isNaN() 提供了一种检查与 NaN 是否相等的便捷方法。请注意，你无法使用 == 或 === 运算符来测试与 NaN 是否相等，因为与 JavaScript 中的所有其他值比较不同，每当一个操作数为 NaN 时，即使另一个操作数也是 NaN，这些操作也会计算为 false。

¥The function Number.isNaN() provides a convenient way to check for equality with NaN. Note that you cannot test for equality with NaN using either the == or === operators, because unlike all other value comparisons in JavaScript, these evaluate to false whenever one operand is NaN, even if the other operand is also NaN.

由于在所有可能的 JavaScript 值中，x !== x 仅适用于 NaN，因此 Number.isNaN(x) 也可以替换为 x !== x 的测试，尽管后者可读性较差。

¥Since x !== x is only true for NaN among all possible JavaScript values, Number.isNaN(x) can also be replaced with a test for x !== x, despite the latter being less readable.

与全局 isNaN() 函数相反，Number.isNaN() 方法不会将参数强制转换为数字。这使得传递通常会转换为 NaN 但实际上与 NaN 不同的值变得安全。这也意味着只有同样是 NaN 的 Number 类型值才会返回 true。

¥As opposed to the global isNaN() function, the Number.isNaN() method doesn't force-convert the parameter to a number. This makes it safe to pass values that would normally convert to NaN but aren't actually the same value as NaN. This also means that only values of the Number type that are also NaN return true.

¥Examples

¥Using isNaN()

Number.isNaN(NaN); // true
Number.isNaN(Number.NaN); // true
Number.isNaN(0 / 0); // true
Number.isNaN(37); // false

¥Difference between Number.isNaN() and global isNaN()

Number.isNaN() 不会尝试将参数转换为数字，因此非数字始终返回 false。以下均为 false：

¥Number.isNaN() doesn't attempt to convert the parameter to a number, so non-numbers always return false. The following are all false:

Number.isNaN("NaN");
Number.isNaN(undefined);
Number.isNaN({});
Number.isNaN("blabla");
Number.isNaN(true);
Number.isNaN(null);
Number.isNaN("37");
Number.isNaN("37.37");
Number.isNaN("");
Number.isNaN(" ");

全局 isNaN() 将其参数强制为数字：

¥The global isNaN() coerces its parameter to a number:

isNaN("NaN"); // true
isNaN(undefined); // true
isNaN({}); // true
isNaN("blabla"); // true
isNaN(true); // false, this is coerced to 1
isNaN(null); // false, this is coerced to 0
isNaN("37"); // false, this is coerced to 37
isNaN("37.37"); // false, this is coerced to 37.37
isNaN(""); // false, this is coerced to 0
isNaN(" "); // false, this is coerced to 0

¥See also

• core-js 中 Number.isNaN 的 Polyfill
• Number
• isNaN()