javascript记忆

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