JS 的MID 该怎么写？

[monlee]

在javascript中，与vbscript中left(),right,mid()功能相同的函数是什么?

//字符串左取
String.prototype.left = function(num,mode){if(!/\d+/.test(num))return(this);var str = this.substr(0,num);if(!mode) return str;var n = str.Tlength() - str.length;num = num - parseInt(n/2);return this.substr(0,num);}
//字符串右取
String.prototype.right = function(num,mode){if(!/\d+/.test(num))return(this);var str = this.substr(this.length-num);if(!mode) return str;var n = str.Tlength() - str.length;num = num - parseInt(n/2);return this.substr(this.length-num);}

Mid 该怎么写呢？盼打救！！谢谢各位大侠！！

[Dogfish]

substring

[hookee]

String.prototype.mid=function(start, len){
    if(isNaN(start)) start=0;
    if(isNaN(len)) len=0;
    return this.substr(start-1,len);
}

[银狐被占用]

var s="abc";
document.writeln(s.substring(1,1));

[monlee]

已解决了，谢谢大家

[wxeddy]

解决了不贴出来 谁知道你是怎么解决的？真是服了！！！！！！！