js中“原生”map

var map = {}; // Map map = new HashMap();  
map[key] = value; // map.put(key, value);  
var value = map[key]; // Object value = map.get(key);  
var has = key in map; // boolean has = map.containsKey(key);  
delete map[key]; // map.remove(key);  
// 遍历    
for(key in map){    
    alert(key + map[key]);    
}    
//长度判断  
var length  = Object.keys(map).length ;