Math.round()

¥Syntax

Math.round(x)

¥Parameters

x

一个号码。

¥Return value

x 的值四舍五入到最接近的整数。

¥The value of x rounded to the nearest integer.

¥Description

如果参数的小数部分大于 0.5，则参数将四舍五入为具有下一个较高绝对值的整数。如果小于 0.5，则参数四舍五入为绝对值较小的整数。如果小数部分恰好为 0.5，则参数将按 +∞ 方向四舍五入到下一个整数。

¥If the fractional portion of the argument is greater than 0.5, the argument is rounded to the integer with the next higher absolute value. If it is less than 0.5, the argument is rounded to the integer with the lower absolute value. If the fractional portion is exactly 0.5, the argument is rounded to the next integer in the direction of +∞.

注意：这与许多语言的 round() 函数不同，后者通常从零开始舍入半增量，在小数部分恰好为 0.5 的负数情况下给出不同的结果。

¥Note: This differs from many languages' round() functions, which often round half-increments away from zero, giving a different result in the case of negative numbers with a fractional part of exactly 0.5.

Math.round(x) 与 Math.floor(x + 0.5) 并不完全相同。当 x 为 -0 或 -0.5 ≤ x < 0 时，Math.round(x) 返回 -0，而 Math.floor(x + 0.5) 返回 0。然而，忽略差异和潜在的精度误差，Math.round(x) 和 Math.floor(x + 0.5) 通常是等效的。

¥Math.round(x) is not exactly the same as Math.floor(x + 0.5). When x is -0, or -0.5 ≤ x < 0, Math.round(x) returns -0, while Math.floor(x + 0.5) returns 0. However, neglecting that difference and potential precision errors, Math.round(x) and Math.floor(x + 0.5) are generally equivalent.

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

¥Because round() is a static method of Math, you always use it as Math.round(), rather than as a method of a Math object you created (Math has no constructor).

¥Examples

¥Using round

Math.round(-Infinity); // -Infinity
Math.round(-20.51); // -21
Math.round(-20.5); // -20
Math.round(-0.1); // -0
Math.round(0); // 0
Math.round(20.49); // 20
Math.round(20.5); // 21
Math.round(42); // 42
Math.round(Infinity); // Infinity

¥See also

• Number.prototype.toPrecision()
• Number.prototype.toFixed()
• Math.abs()
• Math.ceil()
• Math.floor()
• Math.sign()
• Math.trunc()