Javascript Hashtable

I can't remember where did I find this so I cannot put the reference here.

function Hashtable(){
    this.clear = hashtable_clear;
    this.containsKey = hashtable_containsKey;
    this.containsValue = hashtable_containsValue;
    this.get = hashtable_get;
    this.isEmpty = hashtable_isEmpty;
    this.keys = hashtable_keys;
    this.put = hashtable_put;
    this.remove = hashtable_remove;
    this.size = hashtable_size;
    this.toString = hashtable_toString;
    this.values = hashtable_values;
    this.hashtable = new Array();
}                
/*=======Private methods for internal use only========*/

function hashtable_clear(){
    this.hashtable = new Array();
}

function hashtable_containsKey(key){
    var exists = false;
    for (var i in this.hashtable) {
        if (i == key && this.hashtable[i] != null) {
            exists = true;
            break;
        }
    }
    return exists;
}

function hashtable_containsValue(value){
    var contains = false;
    if (value != null) {
        for (var i in this.hashtable) {
            if (this.hashtable[i] == value) {
                contains = true;
                break;
            }
        }
    }
    return contains;
}

function hashtable_get(key){
    return this.hashtable[key];
}

function hashtable_isEmpty(){
    return (this.size == 0) ? true : false;
}

function hashtable_keys(){
    var keys = new Array();
    for (var i in this.hashtable) {
        if (this.hashtable[i] != null) 
            keys.push(i);
    }
    return keys;
}

function hashtable_put(key, value){
    if (key == null || value == null) {
        throw 'NullPointerException {' + key + '},{' + value + '}';
    }else{
        this.hashtable[key] = value;
    }
}

function hashtable_remove(key){
    var rtn = this.hashtable[key];
    this.hashtable[key] = null;
    return rtn;
}

function hashtable_size(){
    var size = 0;
    for (var i in this.hashtable) {
        if (this.hashtable[i] != null) 
            size ++;
    }
    return size;
}

function hashtable_toString(){
    var result = '';
    for (var i in this.hashtable)
    {      
        if (this.hashtable[i] != null) 
            result += '{' + i + '},{' + this.hashtable[i] + '}\n';   
    }
    return result;
}

function hashtable_values(){
    var values = new Array();
    for (var i in this.hashtable) {
        if (this.hashtable[i] != null) 
            values.push(this.hashtable[i]);
    }
    return values;
}