以下内容是否会使对象满足枚举在JavaScript中的所有特性?类似于:

my.namespace.ColorEnum = {
  RED : 0,
  GREEN : 1,
  BLUE : 2
}

// later on

if(currentColor == my.namespace.ColorEnum.RED) {
  // whatever
}

还是有其他方法可以做到这一点?


当前回答

阅读了所有的答案,没有找到任何非冗长和干燥的解决方案。我使用这一行:

const modes = ['DRAW', 'SCALE', 'DRAG'].reduce((o, v) => ({ ...o, [v]: v }), {});

它生成具有人类可读值的对象:

{
  DRAW: 'DRAW',
  SCALE: 'SCALE',
  DRAG: 'DRAG'
}

其他回答

我提出了一种以Java中的枚举为模型的方法。这些是类型安全的,因此您也可以执行instanceof检查。

可以这样定义枚举:

var Days = Enum.define("Days", ["Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday", "Sunday"]);

Days现在引用Days枚举:

Days.Monday instanceof Days; // true

Days.Friday.name(); // "Friday"
Days.Friday.ordinal(); // 4

Days.Sunday === Days.Sunday; // true
Days.Sunday === Days.Friday; // false

Days.Sunday.toString(); // "Sunday"

Days.toString() // "Days { Monday, Tuesday, Wednesday, Thursday, Friday, Saturday, Sunday } "

Days.values().map(function(e) { return e.name(); }); //["Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday", "Sunday"]
Days.values()[4].name(); //"Friday"

Days.fromName("Thursday") === Days.Thursday // true
Days.fromName("Wednesday").name() // "Wednesday"
Days.Friday.fromName("Saturday").name() // "Saturday"

实施:

var Enum = (function () {
    /**
     * Function to define an enum
     * @param typeName - The name of the enum.
     * @param constants - The constants on the enum. Can be an array of strings, or an object where each key is an enum
     * constant, and the values are objects that describe attributes that can be attached to the associated constant.
     */
    function define(typeName, constants) {

        /** Check Arguments **/
        if (typeof typeName === "undefined") {
            throw new TypeError("A name is required.");
        }

        if (!(constants instanceof Array) && (Object.getPrototypeOf(constants) !== Object.prototype)) {

            throw new TypeError("The constants parameter must either be an array or an object.");

        } else if ((constants instanceof Array) && constants.length === 0) {

            throw new TypeError("Need to provide at least one constant.");

        } else if ((constants instanceof Array) && !constants.reduce(function (isString, element) {
                return isString && (typeof element === "string");
            }, true)) {

            throw new TypeError("One or more elements in the constant array is not a string.");

        } else if (Object.getPrototypeOf(constants) === Object.prototype && !Object.keys(constants).reduce(function (isObject, constant) {
                return Object.getPrototypeOf(constants[constant]) === Object.prototype;
            }, true)) {

            throw new TypeError("One or more constants do not have an associated object-value.");

        }

        var isArray = (constants instanceof Array);
        var isObject = !isArray;

        /** Private sentinel-object used to guard enum constructor so that no one else can create enum instances **/
        function __() { };

        /** Dynamically define a function with the same name as the enum we want to define. **/
        var __enum = new Function(["__"],
            "return function " + typeName + "(sentinel, name, ordinal) {" +
                "if(!(sentinel instanceof __)) {" +
                    "throw new TypeError(\"Cannot instantiate an instance of " + typeName + ".\");" +
                "}" +

                "this.__name = name;" +
                "this.__ordinal = ordinal;" +
            "}"
        )(__);

        /** Private objects used to maintain enum instances for values(), and to look up enum instances for fromName() **/
        var __values = [];
        var __dict = {};

        /** Attach values() and fromName() methods to the class itself (kind of like static methods). **/
        Object.defineProperty(__enum, "values", {
            value: function () {
                return __values;
            }
        });

        Object.defineProperty(__enum, "fromName", {
            value: function (name) {
                var __constant = __dict[name]
                if (__constant) {
                    return __constant;
                } else {
                    throw new TypeError(typeName + " does not have a constant with name " + name + ".");
                }
            }
        });

        /**
         * The following methods are available to all instances of the enum. values() and fromName() need to be
         * available to each constant, and so we will attach them on the prototype. But really, they're just
         * aliases to their counterparts on the prototype.
         */
        Object.defineProperty(__enum.prototype, "values", {
            value: __enum.values
        });

        Object.defineProperty(__enum.prototype, "fromName", {
            value: __enum.fromName
        });

        Object.defineProperty(__enum.prototype, "name", {
            value: function () {
                return this.__name;
            }
        });

        Object.defineProperty(__enum.prototype, "ordinal", {
            value: function () {
                return this.__ordinal;
            }
        });

        Object.defineProperty(__enum.prototype, "valueOf", {
            value: function () {
                return this.__name;
            }
        });

        Object.defineProperty(__enum.prototype, "toString", {
            value: function () {
                return this.__name;
            }
        });

        /**
         * If constants was an array, we can the element values directly. Otherwise, we will have to use the keys
         * from the constants object.
         */
        var _constants = constants;
        if (isObject) {
            _constants = Object.keys(constants);
        }

        /** Iterate over all constants, create an instance of our enum for each one, and attach it to the enum type **/
        _constants.forEach(function (name, ordinal) {
            // Create an instance of the enum
            var __constant = new __enum(new __(), name, ordinal);

            // If constants was an object, we want to attach the provided attributes to the instance.
            if (isObject) {
                Object.keys(constants[name]).forEach(function (attr) {
                    Object.defineProperty(__constant, attr, {
                        value: constants[name][attr]
                    });
                });
            }

            // Freeze the instance so that it cannot be modified.
            Object.freeze(__constant);

            // Attach the instance using the provided name to the enum type itself.
            Object.defineProperty(__enum, name, {
                value: __constant
            });

            // Update our private objects
            __values.push(__constant);
            __dict[name] = __constant;
        });

        /** Define a friendly toString method for the enum **/
        var string = typeName + " { " + __enum.values().map(function (c) {
                return c.name();
            }).join(", ") + " } ";

        Object.defineProperty(__enum, "toString", {
            value: function () {
                return string;
            }
        });

        /** Freeze our private objects **/
        Object.freeze(__values);
        Object.freeze(__dict);

        /** Freeze the prototype on the enum and the enum itself **/
        Object.freeze(__enum.prototype);
        Object.freeze(__enum);

        /** Return the enum **/
        return __enum;
    }

    return {
        define: define
    }

})();
var ColorEnum = {
    red: {},
    green: {},
    blue: {}
}

您不需要确保不以这种方式将重复的数字分配给不同的枚举值。一个新对象被实例化并分配给所有枚举值。

从1.8.5开始,可以密封和冻结物体,因此定义如下:

const DaysEnum = Object.freeze({"monday":1, "tuesday":2, "wednesday":3, ...})

or

const DaysEnum = {"monday":1, "tuesday":2, "wednesday":3, ...}
Object.freeze(DaysEnum)

瞧!JS枚举。

然而,这并不能阻止您为变量赋值,这通常是enums的主要目标:

let day = DaysEnum.tuesday
day = 298832342 // goes through without any errors

确保更强的类型安全性(使用enums或其他)的一种方法是使用TypeScript或Flow等工具。

不需要引用,但我保留了它们以保持一致性。

这是我们都想要的:

function Enum(constantsList) {
    for (var i in constantsList) {
        this[constantsList[i]] = i;
    }
}

现在,您可以创建枚举:

var YesNo = new Enum(['NO', 'YES']);
var Color = new Enum(['RED', 'GREEN', 'BLUE']);

通过这样做,可以以通常的方式处理常量(YesNo YES,Color.GREEN),并获得一个连续的int值(NO=0,YES=1;RED=0,GREEN=1,BLUE=2)。

还可以使用Enum.prototype添加方法:

Enum.prototype.values = function() {
    return this.allValues;
    /* for the above to work, you'd need to do
            this.allValues = constantsList at the constructor */
};

编辑-小的改进-现在使用varargs:(不幸的是,它不能在IE:S上正常工作……应该继续使用以前的版本)

function Enum() {
    for (var i in arguments) {
        this[arguments[i]] = i;
    }
}

var YesNo = new Enum('NO', 'YES');
var Color = new Enum('RED', 'GREEN', 'BLUE');

你可以这样做

    var Enum = (function(foo) {

    var EnumItem = function(item){
        if(typeof item == "string"){
            this.name = item;
        } else {
            this.name = item.name;
        }
    }
    EnumItem.prototype = new String("DEFAULT");
    EnumItem.prototype.toString = function(){
        return this.name;
    }
    EnumItem.prototype.equals = function(item){
        if(typeof item == "string"){
            return this.name == item;
        } else {
            return this == item && this.name == item.name;
        }
    }

    function Enum() {
        this.add.apply(this, arguments);
        Object.freeze(this);
    }
    Enum.prototype.add = function() {
        for (var i in arguments) {
            var enumItem = new EnumItem(arguments[i]);
            this[enumItem.name] = enumItem;
        }
    };
    Enum.prototype.toList = function() {
        return Object.keys(this);
    };
    foo.Enum = Enum;
    return Enum;
})(this);
var STATUS = new Enum("CLOSED","PENDING", { name : "CONFIRMED", ackd : true });
var STATE = new Enum("CLOSED","PENDING","CONFIRMED",{ name : "STARTED"},{ name : "PROCESSING"});

如此库中所定义。https://github.com/webmodule/foo/blob/master/foo.js#L217

完整示例https://gist.github.com/lnt/bb13a2fd63cdb8bce85fd62965a20026