字符串的方法详解

1.split(): 将字符串转化为数组，join将数组转化为字符串。不会改变原字符串

var a = "a,b,c,s";
var b = a.split(",");
console.log(a);//a,b,c,s
console.log(b);//["a", "b", "c", "s"]

2.substr(start, length):参数一表示开始的位置，参数二表示提取字符的长度。不会改变原字符串。但start为负数时，length无效。-1为倒数第一个数字，以此类推。

var a = "abcdefg";
var b = a.substr(2,3);
console.log(a);//abcdefg
console.log(b);//cde

3.charAt(): 返回该位置的字符

var a = "abcdefg";
var b = a.charAt(2);
console.log(a);//abcdefg
console.log(b);//c

4.charCodeAt(): 返回位置的字符编码，用于判断字符，例获取字节。

 var a = "abcdefg";
 var b = a.charCodeAt(0);
 console.log(a);//abcdefg
 console.log(b);//97

5.concat: 连接字符

    var a = "a";
    var b = a.concat("b", "c");
    console.log(a);//a
    console.log(b);//abc

6.substring(start, end): 获取字符，不接受负数。

    var a = "abcdefg";
    var b = a.substring(2, 3);
    console.log(a);//abcdefg
    console.log(b);//c

7.indexOf: 返回第一个字符的位置

　　var text = "Mississippi";
    var a = text.indexOf("ss");
    var b = text.indexOf("ss", 3);
    var c = text.indexOf("ss", 6);
    console.log(a);//2
    console.log(b);//5
    console.log(c);//-1

8.lastIndexOf: 从末尾开始查找

    var text = "Mississippi";
    var a = text.lastIndexOf("ss");
    var b = text.lastIndexOf("ss", 5);
    var c = text.lastIndexOf("ss", 6);
    console.log(a);//5
    console.log(b);//2,在[0, 3]范围内找
    console.log(c);//5,在[0, 6]范围内找

9.toLowerCase(): 变为小写

    var a = "aBCDefg";
    var b = a.toLowerCase();
    console.log(a);//aBCDefg
    console.log(b);//abcdefg

10.toUpperCase(): 变为大写

    var a = "aBCDefg";
    var b = a.toUpperCase();
    console.log(a);//aBCDefg
    console.log(b);//ABCDEFG 

11.search()、match()、replace()用法见文章正则表达式

12.slice()用法见文章数组详解