javascript String.indexOf实现

群里abcd提出问题,现在有以下三个实现，欢迎大家参与(注意，为了兼容IE6，不能使用str[i]，要用str.charAt(i);不能使用slice，replace等原生函数)：

GrayZhang的实现

String.prototype.substring = function(start, length) {
    var array = [];
    for (var i = start; i < start + length; i++) {
        array.push(this.charAt(i));
    }
    return array.join();
};
String.prototype.indexOf = function(s) {
    for (var i = 0; i < this.length - s.length; i++) {
        if (this.charAt(i) === s.charAt(0) &&
            this.substring(i, s.length) === s) {
            return i;
        }
    }
    return -1;
};

我的实现：

//by 司徒正美 2011.8.18
String.prototype.indexOf = function(sub){
        var a = sub.charAt(0),an = sub.length,n = this.length;
        if(n == an){
          return this == sub ? 0 : -1
        }
        if(n < an){
          return -1
        }
        loop:
          for(var i=0;i < n;i++){
          if(this.charAt(i) == a){
            for(var j=1;j < an;j++){
              if(this.charAt(j+i) != sub.charAt(j)){
                continue loop
              }
            }
            return i
          }
        }
        return -1;
      }
 
       var a = "aabbccb";
      console.log(a.indexOf("bbccb"))//2
      console.log("Blue Whale".indexOf("Blue") )   // returns 0
      console.log("Blue Whale".indexOf("Blute"))   // returns -1

<p>abcd的实现：</p>
<pre class="brush:js;gutter:false;toolbar:false;">

function indexOf(s, t) {
	if (s.length) {
		var back = false;
		var i = 0;

for (var j = 0; j < t.length; ++j) {
			if (s.charAt(i) != t.charAt(j)) {
				do {
					if (++i >= s.length) return -1;
					if (s.charAt(i) == t.charAt(j)) {
						if (j) back = true;
						break;
					}
				}
				while (true);
			}
			if (back) {
				for (var k = 1; k <= j; k++)
					if (s.charAt(i - k) != t.charAt(j - k))
						continue;
				back = false;
			}
		}
		return i - j + 1;
	}
	return t.length && -1;
} 
</pre>
http://proto.layer51.com/d.aspx?f=32
//---------------------------------------------------------------------------  
String.prototype.charAt = function(index){  
    return(substring(this, index+1, 1));  
}  
  
String.prototype.concat = function(){  
    var r = this.toString();  
    for (var i=0; i<arguments.length; ++i){  
        r += arguments[i];  
    }  
    return (r);  
}  
  
String.prototype.indexOf = function(sub, i){  
    if (i == null) i = 0;  
    var size = sub.length;  
    var last = this.length - size + 1;  
    while ((i <= last) && (substring(this, 1+i++, size) != sub));  
    return (i <= last ? (i-1) : -1);  
}  
  
String.prototype.lastIndexOf = function(sub, i){  
    size = sub.length;  
    i == null ? i = this.length - size + 1 : ++i;  
    if (sub.length == 0) return i-1;  
    while ((i >= 0) && (substring(this, i--, size) != sub));  
    return (i == -1 ? -1 : (i));  
}  
  
String.prototype.slice = function(s, e){  
    return(substring(this, s+1, e-s));  
}  
  
String.prototype.split = function(d){  
    if (d != null){  
        var r = new Array();  
        var size = this.length;  
        var c = 0;  
        var n = 0;  
        if (d != ""){  
            for (var i=0; i<=size; ++i){  
                if (substring(this, i+1, 1) == d){  
                    r[n] = substring(this, c+1, i-c);  
                    c = i+1;  
                    ++n;  
                }  
            }  
            if (c != i){  
                r[n] = substring(this, c+1, i-c);  
            }  
        }else{  
            for (var i=0; i<s; ++i){  
                    r[i] = substring(this, i+1, 1);  
            }         
        }  
    }else{  
        r = new Array(this.toString());  
    }  
    return (r);  
}  
  
String.prototype.substr = function(s, l){  
    if (l == null){  
        l = this.length - s;  
    }  
    return(substring(this, s+1, l));  
}  
String.prototype.toUpperCase = function() {

var r = this.toString();

out = "";

for (x=0; x<r.length; x++) {

upNo = r.charCodeAt(x);

if ((upNo>96 && upNo<123) || (upNo>223 && upNo<254)) {

out += String.fromCharCode(upNo-32);

} else {

out += String.fromCharCode(upNo);

}

return out;

}

String.prototype.toLowerCase = function() {