js中的Map

/*
 * js中的map
 */
function myJsMap() {
    // 定义myMap,并添加值
    var myMap = {};
    myMap["key2"] = "value2";
    myMap["key1"] = "value1";
    myMap["key3"] = "value3";
    // 判断某个值是否在myMap中
    if ("key2" in myMap) {
        alert("key2 = " + myMap["key2"]);
    }
    // 删除myMap中的值
    delete myMap["key2"];
    // 遍历myMap
    for (var key in myMap) {
        // 调试中myMap的键值对显示为按key排序
        // {key1: "value1", key2: "value2", key3: "value3"}
        // 但是实际输出顺序依然为添加的顺序
        // key2=value2,key1=value1,key3=value3
        alert(key + " = " + myMap[key]);
    }
}