JS 数字取整数方式[通俗易懂]

大家好，又见面了，我是你们的朋友全栈君。

1、parseInt(number)

var 
    num1 = parseInt("2015nov"),  //2015
    num2 = parseInt(""),  //NaN
    num3 = parseInt("0xA"),  //10(十六进制)
    num4 = parseInt(20.15),  //20
    num5 = parseInt(-20.15),  //-20
    num6 = parseInt("070");  //56(八进制数)

2、~~number

//所有取整之中最快的，位运算，一如既往的快。
var num1 = ~~20.15,  //20
    num2 = ~~(-20.15);  //-20

3、number^0

var num1 = 20.15^0,  //20
    num2 = (-20.15)^0;  //-20

4、number<<0

var num1 = 20.15 << 0,  //20
    num2 = (-20.15) << 0,  //-20

5、四舍五入Math.round(number)

var num1 = Math.round(20.1),  //20
    num2 = Math.round(20.5),  //21
    num3 = Math.round(20.9),  //21
    num4 = Math.round(-20.1),  //-20
    num5 = Math.round(-20.5),  //-20 注意这里是-20而不是-21
    num6 = Math.round(-20.9);  //-21

6、向上取整Math.ceil(number)

var num1 = Math.ceil(20.1),  //21
    num2 = Math.ceil(20.5),  //21
    num3 = Math.ceil(20.9),  //21
    num4 = Math.ceil(-20.1),  //-20
    num5 = Math.ceil(-20.5),  //-20
    num6 = Math.ceil(-20.9);  //-20
    

7、向下取整Math.floor(number)

var num1 = Math.floor(20.1),  //20
    num2 = Math.floor(20.5),  //20
    num3 = Math.floor(20.9),  //20
    num4 = Math.floor(-20.1),  //-21
    num5 = Math.floor(-20.5),  //-21
    num6 = Math.floor(-20.9),  //-21

做个小笔记记录下方法，好记性不如烂笔头~~