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?
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
我不久前使用了__defineGetter__和__defineSetter__或defineProperty的组合,具体取决于JS版本。
下面是我制作的枚举生成函数:https://gist.github.com/gfarrell/6716853
你可以这样使用:
var Colours = Enum('RED', 'GREEN', 'BLUE');
它将创建一个不可变的字符串:int字典(一个枚举)。
其他回答
我编写了enumeranjs一个非常小的库来解决这个问题,它确保了类型安全,允许枚举常量从原型继承,保证枚举常量和枚举类型是不可变的+许多小特性。它允许重构大量代码,并在枚举定义中移动一些逻辑。下面是一个示例:
var CloseEventCodes = new Enumeration("closeEventCodes", {
CLOSE_NORMAL: { _id: 1000, info: "Connection closed normally" },
CLOSE_GOING_AWAY: { _id: 1001, info: "Connection closed going away" },
CLOSE_PROTOCOL_ERROR: { _id: 1002, info: "Connection closed due to protocol error" },
CLOSE_UNSUPPORTED: { _id: 1003, info: "Connection closed due to unsupported operation" },
CLOSE_NO_STATUS: { _id: 1005, info: "Connection closed with no status" },
CLOSE_ABNORMAL: { _id: 1006, info: "Connection closed abnormally" },
CLOSE_TOO_LARGE: { _id: 1009, info: "Connection closed due to too large packet" }
},{ talk: function(){
console.log(this.info);
}
});
CloseEventCodes.CLOSE_TOO_LARGE.talk(); //prints "Connection closed due to too large packet"
CloseEventCodes.CLOSE_TOO_LARGE instanceof CloseEventCodes //evaluates to true
枚举基本上是一个工厂。
此处提供完整记录的指南。希望这有帮助。
截至2014年10月的撰写,这里有一个当代的解决方案。我将解决方案作为节点模块编写,并使用Mocha和Chai以及undercoreJS进行了测试。您可以很容易地忽略这些,如果愿意,只需使用Enum代码。
看到了很多带有过于复杂的库等的帖子。在Javascript中获得枚举支持的解决方案非常简单,真的不需要。代码如下:
文件:enums.js
_ = require('underscore');
var _Enum = function () {
var keys = _.map(arguments, function (value) {
return value;
});
var self = {
keys: keys
};
for (var i = 0; i < arguments.length; i++) {
self[keys[i]] = i;
}
return self;
};
var fileFormatEnum = Object.freeze(_Enum('CSV', 'TSV'));
var encodingEnum = Object.freeze(_Enum('UTF8', 'SHIFT_JIS'));
exports.fileFormatEnum = fileFormatEnum;
exports.encodingEnum = encodingEnum;
还有一个测试来说明它给你带来了什么:
文件:enumsSpec.js
var chai = require("chai"),
assert = chai.assert,
expect = chai.expect,
should = chai.should(),
enums = require('./enums'),
_ = require('underscore');
describe('enums', function () {
describe('fileFormatEnum', function () {
it('should return expected fileFormat enum declarations', function () {
var fileFormatEnum = enums.fileFormatEnum;
should.exist(fileFormatEnum);
assert('{"keys":["CSV","TSV"],"CSV":0,"TSV":1}' === JSON.stringify(fileFormatEnum), 'Unexpected format');
assert('["CSV","TSV"]' === JSON.stringify(fileFormatEnum.keys), 'Unexpected keys format');
});
});
describe('encodingEnum', function () {
it('should return expected encoding enum declarations', function () {
var encodingEnum = enums.encodingEnum;
should.exist(encodingEnum);
assert('{"keys":["UTF8","SHIFT_JIS"],"UTF8":0,"SHIFT_JIS":1}' === JSON.stringify(encodingEnum), 'Unexpected format');
assert('["UTF8","SHIFT_JIS"]' === JSON.stringify(encodingEnum.keys), 'Unexpected keys format');
});
});
});
正如您所看到的,您获得了一个Enum工厂,只需调用Enum.keys即可获得所有键,并且可以将键本身与整数常量匹配。您可以使用不同的值重用工厂,并使用Node的模块化方法导出生成的Enum。
同样,如果您只是一个普通用户,或者在浏览器等中,只需使用代码的工厂部分,如果您不想在代码中使用下划线库,也可能会删除它。
class Enum {
constructor (...vals) {
vals.forEach( val => {
const CONSTANT = Symbol(val);
Object.defineProperty(this, val.toUpperCase(), {
get () {
return CONSTANT;
},
set (val) {
const enum_val = "CONSTANT";
// generate TypeError associated with attempting to change the value of a constant
enum_val = val;
}
});
});
}
}
用法示例:
const COLORS = new Enum("red", "blue", "green");
您可以使用一个简单的函数来反转键和值,当它将数字整数字符串转换为数字时,它也可以处理数组。代码小、简单,可用于此用例和其他用例。
var objInvert=函数(obj){var反转={}for(对象中的变量i){如果(i.match(/^\d+$/))i=parseInt(i,10)反转[obj[i]]=i}返回反转}var musicStyles=对象冻结(objInvert(['ROCK','SURF','METAL',“BOSSA-NOVA”、“op”、“die”]))console.log(音乐样式)
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
}
})();