先定义一个字符串:
var aString = "you are beautiful,so beautiful,and i love you ver much";
拿到第一个逗号的位置:
var first = aString.indexOf(","); //17
然后去拿第二个逗号的位置:
var second= aString.indexOf(",",first+1); //30
截取两个逗号之间的内容:
var newString = aString.substring(first+1,second);