JavaScript中的枚举标志

Question

我需要在Javascript中模拟枚举类型,方法看起来非常简单:

var MyEnum = {Left = 1; Right = 2; Top = 4; Bottom = 8}

现在,在C#中我可以将这些值组合起来:

MyEnum left_right = MyEnum.Left | MyEnum.Right

然后我可以测试枚举是否具有一定的价值:

if (left_right & MyEnum.Left == MyEnum.Left) {...}

我可以在Javascript中做类似的事情吗？

Answer 1

您只需使用按位运算符:

var myEnum = {
  left: 1,
  right: 2,
  top: 4,
  bottom: 8
}

var myConfig = myEnum.left | myEnum.right;

if (myConfig & myEnum.right) {
  // right flag is set
}

更多信息:

• 理解javascript中的按位运算
• 如何检查我的字节标志？

Answer 2

在javascript中,您应该能够将它们组合为:

var left_right = MyEnum.Left | MyEnum.Right;

然后测试就像你的例子中一样

if ( (left_right & MyEnum.Left) == MyEnum.Left) {...}

Answer 3

是的,按位算术在Javascript中有效.你必须小心它,因为Javascript只有Number数据类型,它实现为浮点类型.但是,对于按位运算,值将转换为带符号的 32位值.所以只要你不尝试使用超过31位,你就没事了.

Answer 4

我在打字稿中实现了：

export class FlagEnumService {

    constructor(private value: number = 0) {
    }

    public get() {
        return this.value;
    }

    public set(value: number): this {
        this.value = value;
        return this;
    }

    public has(key: number): boolean {
        return !!(this.value & key);
    }

    public add(key: number): this {
        this.value |= key;
        return this;
    }

    public delete(key: number): this {
        this.value &= ~key;
        return this;
    }

    public toggle(key: number): this {
        this.has(key) ? this.delete(key) : this.add(key);
        return this;
    }
}

并进行澄清测试

import { FlagEnumService } from './flag-enum.service';

enum Test {
    None = 0,
    First = 1,
    Second = 2,
    Third = 4,
    Four = 8
}

describe('FlagEnumService', () => {
    let service: FlagEnumService;
    beforeEach(() => service = new FlagEnumService());

    it('should create with initial value', () => {
        service = new FlagEnumService(Test.First);
        expect(service.get()).toBe(Test.First);
    });

    it('should return true if has flag', () => {
        service = new FlagEnumService(Test.First);
        expect(service.has(Test.First)).toBe(true);
    });

    it('should return false if doesn\'t have flag', () => {
        service = new FlagEnumService(Test.First);
        expect(service.has(Test.Second)).toBe(false);
    });

    it('should add', () => {
        expect(service.add(Test.First).add(Test.Second).get()).toBe(Test.First + Test.Second);
    });

    it('should not add the same value twice', () => {
        expect(service.add(Test.First).add(Test.First).get()).toBe(Test.First);
    });

    it('should remove', () => {
        expect(
            service
                .add(Test.First)
                .add(Test.Second)
                .delete(Test.Second)
                .get()
        )
            .toBe(Test.First);
    });

    it('should return 0 when add then remove the same value', () => {
        expect(service.add(Test.First).delete(Test.First).get()).toBe(0);
    });

    it('should not remove not added values', () => {
        expect(service.add(Test.First).delete(Test.Second).get()).toBe(Test.First);
    });
});

Answer 5

我试图创建一个示例来演示一个常见的用例,其中可能需要使用位掩码枚举来控制日志记录详细程度.它向我们演示了JavaScript按位操作:在JSFiddle上看到它

/*
 * Demonstration of how a Flags enum can be simulated in JavaScript and 
 * Used to control what gets logged based on user passed value
 */

// A Flags Enum (sort-of)
var LogLevels = {
    NONE: 0,
    INFO: 1,
    TRACE: 2,
    DEBUG: 4,
    WARN: 8,
    ERROR: 16,
    FATAL: 32
};

// Initialize
var currLogLevel = LogLevels.NONE;

// User Sets a log level
var logLevel = LogLevels.WARN;

// Convert the configured logLvel to a bit-masked enum value
switch (logLevel) {
    case LogLevels.INFO:
        currLogLevel = LogLevels.INFO | LogLevels.TRACE | LogLevels.DEBUG | LogLevels.WARN | LogLevels.ERROR | LogLevels.FATAL;
        break;
    case LogLevels.TRACE:
        currLogLevel = LogLevels.TRACE | LogLevels.DEBUG | LogLevels.WARN | LogLevels.ERROR | LogLevels.FATAL;
        break;
    case LogLevels.DEBUG:
        currLogLevel = LogLevels.DEBUG | LogLevels.WARN | LogLevels.ERROR | LogLevels.FATAL;
        break;
    case LogLevels.WARN:
        currLogLevel = LogLevels.WARN | LogLevels.ERROR | LogLevels.FATAL;
        break;
    case LogLevels.ERROR:
    case LogLevels.FATAL:
    default:
        currLogLevel = LogLevels.ERROR | LogLevels.FATAL;
}

// Example: log verbosity set to WARN, so this would NOT be logged
if ((currLogLevel & LogLevels.DEBUG) == LogLevels.DEBUG) {
    console.log("log DEBUG");
}