Math
Math 是一个内置对象， 它具有数学常数和函数的属性和方法。不是一个函数对象。
描述
与其它全局对象不同的是, Math 不是一个构造器. Math 的所有属性和方法都是静态的. 你用到的常数pi可以用 Math.PI 表示,用 x 作参数 Math.sin(x)调用sin函数. JavaScript中的常数, 是以全精度的实数定义的.
属性
Math.E欧拉常数，也是自然对数的底数, 约等于 2.718.Math.LN22的自然对数, 约等于0.693.Math.LN1010的自然对数, 约等于 2.303.Math.LOG2E以2为底E的对数, 约等于 1.443.Math.LOG10E以10为底E的对数, 约等于 0.434.Math.PI圆周率，一个圆的周长和直径之比，约等于 3.14159.Math.SQRT1_21/2的平方根, 约等于 0.707.Math.SQRT22的平方根,约等于 1.414.
方法
需要注意的是三角函数（sin(), cos(), tan(),asin(), acos(), atan(), atan2()）是以弧度返回值的。可以通过除法（Math.PI / 180）把弧度转换为角度，也可以通过其他方法来转换。
需要注意的是很多数学函数都有一个精度，并且精度在不同环境下也是不相同的。这就意味着不同的浏览器会给出不同的结果，甚至相同的 JS 引擎在不同的OS或者架构下也会给出不同的结果。
Math.abs(x)返回x的绝对值.
Math.acos(x)返回x的反余弦值.
Math.acosh(x)返回x的反双曲余弦值.
Math.asin(x)返回x的反正弦值.
Math.asinh(x)返回x的反双曲正弦值.
Math.atan(x)以介于 -PI/2 与 PI/2 弧度之间的数值来返回 x 的反正切值.
Math.atanh(x)返回 x 的反双曲正切值.
Math.atan2(y, x)返回 y/x 的反正切值.
Math.cbrt(x)返回x的立方根.
Math.ceil(x)返回x向上取整后的值.
Math.clz32(x)返回一个32位整数的前导零的数量。
Math.cos(x)返回x的余弦值.
Math.cosh(x)返回x的双曲余弦值.
Math.exp(x)返回 Ex, 当x为参数, E 是欧拉常数 (2.718...), 自然对数的底.
Math.expm1(x)返回 exp(x)-1 的值.
Math.floor(x)返回小于x的最大整数。
Math.fround(x)返回数字的最接近的单精度浮点型表示。
Math.hypot([x[,y[,…]]])返回其参数平方和的平方根。
Math.imul(x)返回32位整数乘法的结果。
Math.log(x)返回一个数的自然对数（loge，即ln）。
Math.log1p(x)返回 1 加上一个数字的的自然对数（loge，即ln）。
Math.log10(x)返回以10为底数的x的对数。
Math.log2(x)返回以2为底数的x的对数。
Math.max([x[,y[,…]]])返回0个到多个数值中最大值.
Math.min([x[,y[,…]]])返回0个到多个数值中最小值.
Math.pow(x,y)返回x的y次幂.
Math.random()返回0到1之间的伪随机数.
Math.round(x)返回四舍五入后的整数.
Math.sign(x)返回x的符号函数, 判定x是正数,负数还是0.
Math.sin(x)返回正弦值.
Math.sinh(x)返回x的双曲正弦值.
Math.sqrt(x)返回x的平方根.
Math.tan(x)返回x的正切值.
Math.tanh(x)返回x的双曲正切值.Math.toSource()返回字符串 "Math".
Math.trunc(x)返回x的整数部分,去除小数.
扩展Math对象
由于JavaScript中的大多数内置Math对象都可以使用自定义属性和方法进行扩展。为了扩展Math对象，你不要使用“原型”而是直接扩展Math：
Math.propName = propValue;
Math.methodName = methodRef;例如，下面的示例向Math对象添加一个方法来计算参数列表的最大公约数。
/* Variadic function -- Returns the greatest common divisor of a list of arguments */
Math.gcd = function () {
var d = Math.min.apply(Math, arguments);
for (let n = arguments.length, i = 0; d > 1 && n > i; arguments[i] % d === 0 ? i++ : (d--, i = 0));
return d;
}尝试一下：
console.log(Math.gcd(20, 30, 15, 70, 40)); // `5`规范
Specification | Status | Comment |
|---|---|---|
ECMAScript 1st Edition (ECMA-262) | Standard | Initial definition. Implemented in JavaScript 1.1. |
ECMAScript 5.1 (ECMA-262)The definition of 'Math' in that specification. | Standard | |
ECMAScript 2015 (6th Edition, ECMA-262)The definition of 'Math' in that specification. | Standard | New methods log10(), log2(), log1p(), expm1(), cosh(), sinh(), tanh(), acosh(), asinh(), atanh(), hypot(), trunc(), sign(), imul(), fround(), cbrt() and clz32() added. |
ECMAScript Latest Draft (ECMA-262)The definition of 'Math' in that specification. | Living Standard | |
浏览器兼容性
Feature | Chrome | Edge | Firefox | Internet Explorer | Opera | Safari |
|---|---|---|---|---|---|---|
E | (Yes) | (Yes) | (Yes) | (Yes) | (Yes) | (Yes) |
LN2 | (Yes) | (Yes) | (Yes) | (Yes) | (Yes) | (Yes) |
LN10 | (Yes) | (Yes) | (Yes) | (Yes) | (Yes) | (Yes) |
LOG2E | (Yes) | (Yes) | (Yes) | (Yes) | (Yes) | (Yes) |
LOG10E | (Yes) | (Yes) | (Yes) | (Yes) | (Yes) | (Yes) |
PI | (Yes) | (Yes) | (Yes) | (Yes) | (Yes) | (Yes) |
SQRT1_2 | (Yes) | (Yes) | (Yes) | (Yes) | (Yes) | (Yes) |
SQRT2 | (Yes) | (Yes) | (Yes) | (Yes) | (Yes) | (Yes) |
abs | (Yes) | (Yes) | (Yes) | (Yes) | (Yes) | (Yes) |
acos | (Yes) | (Yes) | (Yes) | (Yes) | (Yes) | (Yes) |
acosh | 38 | (Yes) | 25 | No | 25 | 7.1 |
asin | (Yes) | (Yes) | (Yes) | (Yes) | (Yes) | (Yes) |
asinh | 38 | (Yes) | 25 | No | 25 | 7.1 |
atan | (Yes) | (Yes) | (Yes) | (Yes) | (Yes) | (Yes) |
atan2 | (Yes) | (Yes) | (Yes) | (Yes) | (Yes) | (Yes) |
atanh | 38 | (Yes) | 25 | No | 25 | 7.1 |
cbrt | 38 | (Yes) | 25 | No | 25 | 7.1 |
ceil | (Yes) | (Yes) | (Yes) | (Yes) | (Yes) | (Yes) |
clz32 | 38 | (Yes) | 31 | No | 25 | (Yes) |
cos | (Yes) | (Yes) | (Yes) | (Yes) | (Yes) | (Yes) |
cosh | 38 | (Yes) | 25 | No | 25 | 7.1 |
exp | (Yes) | (Yes) | (Yes) | (Yes) | (Yes) | (Yes) |
expm1 | 38 | (Yes) | 25 | No | 25 | 7.1 |
floor | (Yes) | (Yes) | (Yes) | (Yes) | (Yes) | (Yes) |
fround | 38 | (Yes) | 26 | No | 25 | 7.1 |
hypot | 38 | (Yes) | 27 | No | 25 | 7.1 |
imul | 28 | (Yes) | 20 | No | 16 | 7 |
log | (Yes) | (Yes) | (Yes) | (Yes) | (Yes) | (Yes) |
log1p | 38 | (Yes) | 25 | No | 25 | 7.1 |
log2 | 38 | (Yes) | 25 | No | 25 | 7.1 |
log10 | 38 | (Yes) | 25 | No | 25 | 7.1 |
max | (Yes) | (Yes) | (Yes) | (Yes) | (Yes) | (Yes) |
min | (Yes) | (Yes) | (Yes) | (Yes) | (Yes) | (Yes) |
pow | (Yes) | (Yes) | (Yes) | (Yes) | (Yes) | (Yes) |
random | (Yes) | (Yes) | (Yes) | (Yes) | (Yes) | (Yes) |
round | (Yes) | (Yes) | (Yes) | (Yes) | (Yes) | (Yes) |
sign | 38 | (Yes) | 25 | No | 25 | 9 |
sin | (Yes) | (Yes) | (Yes) | (Yes) | (Yes) | (Yes) |
sinh | 38 | (Yes) | 25 | No | 25 | 7.1 |
sqrt | (Yes) | (Yes) | (Yes) | (Yes) | (Yes) | (Yes) |
tan | (Yes) | (Yes) | (Yes) | (Yes) | (Yes) | (Yes) |
tanh | 38 | (Yes) | 25 | No | 25 | 7.1 |
trunc | 38 | (Yes) | 25 | No | 25 | 7.1 |
Feature | Android | Chrome for Android | Edge mobile | Firefox for Android | IE mobile | Opera Android | iOS Safari |
|---|---|---|---|---|---|---|---|
E | (Yes) | (Yes) | (Yes) | (Yes) | (Yes) | (Yes) | (Yes) |
LN2 | (Yes) | (Yes) | (Yes) | (Yes) | (Yes) | (Yes) | (Yes) |
LN10 | (Yes) | (Yes) | (Yes) | (Yes) | (Yes) | (Yes) | (Yes) |
LOG2E | (Yes) | (Yes) | (Yes) | (Yes) | (Yes) | (Yes) | (Yes) |
LOG10E | (Yes) | (Yes) | (Yes) | (Yes) | (Yes) | (Yes) | (Yes) |
PI | (Yes) | (Yes) | (Yes) | (Yes) | (Yes) | (Yes) | (Yes) |
SQRT1_2 | (Yes) | (Yes) | (Yes) | (Yes) | (Yes) | (Yes) | (Yes) |
SQRT2 | (Yes) | (Yes) | (Yes) | (Yes) | (Yes) | (Yes) | (Yes) |
abs | (Yes) | (Yes) | (Yes) | (Yes) | (Yes) | (Yes) | (Yes) |
acos | (Yes) | (Yes) | (Yes) | (Yes) | (Yes) | (Yes) | (Yes) |
acosh | (Yes) | (Yes) | (Yes) | 25 | No | (Yes) | 8 |
asin | (Yes) | (Yes) | (Yes) | (Yes) | (Yes) | (Yes) | (Yes) |
asinh | (Yes) | (Yes) | (Yes) | 25 | No | (Yes) | 8 |
atan | (Yes) | (Yes) | (Yes) | (Yes) | (Yes) | (Yes) | (Yes) |
atan2 | (Yes) | (Yes) | (Yes) | (Yes) | (Yes) | (Yes) | (Yes) |
atanh | (Yes) | (Yes) | (Yes) | 25 | No | (Yes) | 8 |
cbrt | (Yes) | (Yes) | (Yes) | 25 | No | (Yes) | 8 |
ceil | (Yes) | (Yes) | (Yes) | (Yes) | (Yes) | (Yes) | (Yes) |
clz32 | (Yes) | (Yes) | (Yes) | 31 | No | (Yes) | (Yes) |
cos | (Yes) | (Yes) | (Yes) | (Yes) | (Yes) | (Yes) | (Yes) |
cosh | (Yes) | (Yes) | (Yes) | 25 | No | (Yes) | 8 |
exp | (Yes) | (Yes) | (Yes) | (Yes) | (Yes) | (Yes) | (Yes) |
expm1 | (Yes) | (Yes) | (Yes) | 25 | No | (Yes) | 8 |
floor | (Yes) | (Yes) | (Yes) | (Yes) | (Yes) | (Yes) | (Yes) |
fround | (Yes) | (Yes) | (Yes) | 26 | No | (Yes) | 8 |
hypot | (Yes) | (Yes) | (Yes) | 27 | No | (Yes) | 8 |
imul | (Yes) | (Yes) | (Yes) | 20 | No | (Yes) | 7 |
log | (Yes) | (Yes) | (Yes) | (Yes) | (Yes) | (Yes) | (Yes) |
log1p | (Yes) | (Yes) | (Yes) | 25 | No | (Yes) | 8 |
log2 | (Yes) | (Yes) | (Yes) | 25 | No | (Yes) | 8 |
log10 | (Yes) | (Yes) | (Yes) | 25 | No | (Yes) | 8 |
max | (Yes) | (Yes) | (Yes) | (Yes) | (Yes) | (Yes) | (Yes) |
min | (Yes) | (Yes) | (Yes) | (Yes) | (Yes) | (Yes) | (Yes) |
pow | (Yes) | (Yes) | (Yes) | (Yes) | (Yes) | (Yes) | (Yes) |
random | (Yes) | (Yes) | (Yes) | (Yes) | (Yes) | (Yes) | (Yes) |
round | (Yes) | (Yes) | (Yes) | (Yes) | (Yes) | (Yes) | (Yes) |
sign | (Yes) | (Yes) | (Yes) | 25 | No | (Yes) | (Yes) |
sin | (Yes) | (Yes) | (Yes) | (Yes) | (Yes) | (Yes) | (Yes) |
sinh | (Yes) | (Yes) | (Yes) | 25 | No | (Yes) | 8 |
sqrt | (Yes) | (Yes) | (Yes) | (Yes) | (Yes) | (Yes) | (Yes) |
tan | (Yes) | (Yes) | (Yes) | (Yes) | (Yes) | (Yes) | (Yes) |
tanh | (Yes) | (Yes) | (Yes) | 25 | No | (Yes) | 8 |
trunc | (Yes) | (Yes) | (Yes) | 25 | No | (Yes) | 8 |
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