javascript实现与后端相同的枚举Enum对象

;
(function (global, undefined) {
    
    global.Enum = function (namesToValues) {
        var enumeration = function () {
            throw "can't Instantiate Enumerations";
        };
        enumeration.setValue = function (x) {
            var val = null;
            enumeration.foreach(function (i) {
                if (i.value == x) {
                    val = enumeration[i.name];
                }
            }, null);
            return val;
        };

        function inherit(superCtor) {
            var f = function () {
            };
            f.prototype = superCtor;
            var ctor = function () {
            };
            ctor.prototype = new f();
            ctor.prototype.constructor = superCtor.constructor;
            return new ctor;
        }

        var proto = enumeration.prototype = {
            constructor: enumeration,
            toString: function () {
                return this.name;
            },
            valueOf: function () {
                return this.value;
            },
            toJSON: function () {
                return this.name;
            }
        };

        enumeration.values = [];

        for (name in namesToValues) {
            var e = inherit(proto);
            e.name = name;
            e.value = namesToValues[name];
            enumeration[name] = e;
            enumeration.values.push(e);

        }

        enumeration.foreach = function (f, c) {
            for (var i = 0; i < this.values.length; i++) {
                f.call(c, this.values[i]);
            }
        };

        return enumeration;

    };
})(window);

var Qos = window.Enum({
            AT_MOST_ONCE: 0,
            AT_LEAST_ONCE: 1,
            EXACTLY_ONCE: 2,
            DEFAULT: 3
        });

现在我们打印Qos.AT_MOST_ONCE会现实一个对象，但是当我们进行 Qos.AT_MOST_ONCE==1 比较时为true；而且Qos.setValue(1) 与 Qos.AT_MOST_ONCE相同

Qos.AT_MOST_ONCE.toString() -> 'AT_MOST_ONCE' ; Qos.AT_MOST_ONCE.valueOf() -> 1 ; Qos.AT_MOST_ONCE.name -> 'AT_MOST_ONCE' ; Qos.AT_MOST_ONCE .value -> 1;

好，现在一个特点与后端语言特性相同的Enum对象就此出现了！！！