JS中map的定义与使用

function Map() {     
    /** 存放键的数组(遍历用到) */    
    this.keys = new Array();     
    /** 存放数据 */    
    this.data = new Object();     
         
    /**   
     * 放入一个键值对   
     * @param {String} key   
     * @param {Object} value   
     */    
    this.put = function(key, value) {     
        if(this.data[key] == null){     
            this.keys.push(key);     
        }     
        this.data[key] = value;     
    };     
         
    /**   
     * 获取某键对应的值   
     * @param {String} key   
     * @return {Object} value   
     */    
    this.get = function(key) {     
        return this.data[key];     
    };     
         
    /**   
     * 删除一个键值对   
     * @param {String} key   
     */    
    this.remove = function(key) {     
        this.keys.remove(key);     
        this.data[key] = null;     
    };     
         
    /**   
     * 遍历Map,执行处理函数   
     *    
     * @param {Function} 回调函数 function(key,value,index){..}   
     */    
    this.each = function(fn){     
        if(typeof fn != 'function'){     
            return;     
        }     
        var len = this.keys.length;     
        for(var i=0;i<len;i++){     
            var k = this.keys[i];     
            fn(k,this.data[k],i);     
        }     
    };     
         
    /**   
     * 获取键值数组(类似Java的entrySet())   
     * @return 键值对象{key,value}的数组   
     */    
    this.entrys = function() {     
        var len = this.keys.length;     
        var entrys = new Array(len);     
        for (var i = 0; i < len; i++) {     
            entrys[i] = {     
                key : this.keys[i],     
                value : this.data[i]     
            };     
        }     
        return entrys;     
    };     
         
    /**   
     * 判断Map是否为空   
     */    
    this.isEmpty = function() {     
        return this.keys.length == 0;     
    };     
         
    /**   
     * 获取键值对数量   
     */    
    this.size = function(){     
        return this.keys.length;     
    };     
         
    /**   
     * 重写toString    
     */    
    this.toString = function(){     
        var s = "{";     
        for(var i=0;i<this.keys.length;i++,s+=','){     
            var k = this.keys[i];     
            s += k+"="+this.data[k];     
        }     
        s+="}";     
        return s;     
    };     
}

这里举例简单的 map.each（）方法 求和计算

var map = new Map();
map.put("a",5);
map.put("b",10);
map.put("c",15);
map.put("d",20);
var sum = 0;
if(map.size()>0){
  map.each(function(e_key, e_value, e_i){
  sum = sum + e_value;
 });
}