Math.round()和ToFixed()
Math.round(1.6)=2
Math.round(-1.4)=-1
var k = 1.74.toFixed(1), m = 1.75.toFixed(1), n = 1.76.toFixed(1),i=-1.49.ToFixed(1); 结果 1.7,1.8,1.8,-1.5
当为负数时round得到的结果可能不是我们想要的所以需要添加绝对值
| num | Math.floor | Math.round | Math.ceil |
| 1.4 | 1 | 1 | 2 |
| 1.5 | 1 | 2 | 2 |
| 1.6 | 1 | 2 | 2 |
| -1.4 | -2 | -1 | -1 |
| -1.5 | -2 | -1 | -1 |
| -1.6 | -2 | -2 | -1 |
substring(start,end)和substr(start,total)
var s1 = new String("010-9898999");
alert(s1.substring(1,4)); //10-
alert(s1.substr(1,4));//10-9