字符串的常用方法

1.substr(start,length) 抽取从 start 下标开始的指定数目的字符

stringObject.substr(start,length)

var str = "hello world";
var a = str.substr(0,3);
console.log(a) //hel

2.substring(start,end) //不接受负数

slice(start,end)

提取两个下标之间的字符
特点:不包含最后一项

var str = "hello";
var b = str.substring(1,4);
console.log(b); //ell

3.charAt(index); 返回指定位置的字符

stringObject.charAt(index)

var str= "hello";
var a = str.charAt(1);
console.log(a); //e;

4.split(); 把一个字符串分割成字符串数组

stringObject.split(separator,howmany)

var str = "hello";
var a = str.split("");
console.log(a);  //["h","e","l","l","0"]

var str = "hello";
var a = str.split("",3);
console.log(a);  //["h","e","l"]

5.match(); 方法可在字符串内检索指定的值，或找到一个或多个正则表达式的匹配

var str="hello world 312312";
var a = str.match(/\d+/g);
console.log(a);  //["312312"]