js写的Hashtable类

<script language="javascript" type="text/javascript">
function Hashtable()
{
this._hash = new Object();
this.add = function(key,value){
if(typeof(key)!="undefined"){
if(this.contains(key)==false){
this._hash[key]=typeof(value)=="undefined"?null:value;
return true;
} else {
return false;
}
} else {
return false;
}
}
this.remove = function(key){delete this._hash[key];}
this.count = function(){var i=0;for(var k in this._hash){i++;} return i;}
this.items = function(key){return this._hash[key];}
this.contains = function(key){ return typeof(this._hash[key])!="undefined";}
this.clear = function(){for(var k in this._hash){delete this._hash[k];}}
}
var a = new Hashtable();
a.add("aa");
a.add("bb",2342);
a.add("bb",2342);
a.remove("aa");
alert(a.count());
alert(a.contains("bb"));
alert(a.contains("aa"));
alert(a.items("bb"));
</script>