Math.fround()

¥Syntax

Math.fround(doubleFloat)

¥Parameters

doubleFloat

一个号码。

¥Return value

doubleFloat 最接近的 32 位单精度 浮点表示。

¥The nearest 32-bit single precision float representation of doubleFloat.

¥Description

JavaScript 内部使用 64 位双浮点数，提供非常高的精度。但是，有时你可能会使用 32 位浮点数，例如，如果你正在从 Float32Array 读取值。这可能会造成混乱：即使数字看起来相同，检查 64 位浮点数和 32 位浮点数是否相等也可能会失败。

¥JavaScript uses 64-bit double floating-point numbers internally, which offer a very high precision. However, sometimes you may be working with 32-bit floating-point numbers, for example if you are reading values from a Float32Array. This can create confusion: checking a 64-bit float and a 32-bit float for equality may fail even though the numbers are seemingly identical.

为了解决这个问题，可以使用 Math.fround() 将 64 位浮点数转换为 32 位浮点数。在内部，JavaScript 继续将数字视为 64 位浮点数，它只是对尾数的第 23 位执行 "四舍五入到偶数"，并将所有后续尾数位设置为 0。如果数字超出 32 位浮点数的范围，则返回 Infinity 或 -Infinity。

¥To solve this, Math.fround() can be used to cast the 64-bit float to a 32-bit float. Internally, JavaScript continues to treat the number as a 64-bit float, it just performs a "round to even" on the 23rd bit of the mantissa, and sets all following mantissa bits to 0. If the number is outside the range of a 32-bit float, Infinity or -Infinity is returned.

因为 fround() 是 Math 的静态方法，所以你始终将其用作 Math.fround()，而不是用作你创建的 Math 对象的方法（Math 不是构造函数）。

¥Because fround() is a static method of Math, you always use it as Math.fround(), rather than as a method of a Math object you created (Math is not a constructor).

¥Examples

¥Using Math.fround()

数字 1.5 可以在二进制数字系统中精确表示，并且在 32 位和 64 位中是相同的：

¥The number 1.5 can be precisely represented in the binary numeral system, and is identical in 32-bit and 64-bit:

Math.fround(1.5); // 1.5
Math.fround(1.5) === 1.5; // true

然而，数字 1.337 无法在二进制数字系统中精确表示，因此它在 32 位和 64 位中有所不同：

¥However, the number 1.337 cannot be precisely represented in the binary numeral system, so it differs in 32-bit and 64-bit:

Math.fround(1.337); // 1.3370000123977661
Math.fround(1.337) === 1.337; // false

$2^150$

对于 32 位浮点数来说太大，因此返回 Infinity：

¥is too big for a 32-bit float, so Infinity is returned:

2 ** 150; // 1.42724769270596e+45
Math.fround(2 ** 150); // Infinity

¥See also

• core-js 中 Math.fround 的 Polyfill
• Math.round()