JavaScript 实现Map效果

var map = {}; // 类似：Map map = new HashMap();
map[key] = value; // 类似：map.put(key, value);
var value = map[key]; // 类似：Object value = map.get(key);
var has = key in map; // 类似：boolean has = map.containsKey(key);
delete map[key]; // 类似：map.remove(key);