打字稿中枚举的意义是什么 [英] what is the significant of enum in typescript

问题描述

打字稿中枚举的用途是什么.如果它的目的只是为了使代码可红，我们就不能为了同样的目的使用常量

what is use of enum in typescript. If it's purpose is only to make code redable can't we just use constant for same purpose

enum Color {
Red = 1, Green = 2, Blue = 4
};


let obj1: Color = Color.Red;
obj1 = 100; // does not show any error in IDE while enum should accept some specific values

如果没有typechecking的优势，难道就不能这么写吗

If there is no advantage of typechecking, Can't it be just written as.

const BasicColor = {
    Red: 1,
    Green: 2,
    Blue: 4
};

let obj2 = BasicColor.Red;

推荐答案

首先在下面:

const BasicColor = {
    Red: 1,
    Green: 2,
    Blue: 4
};

Red、Green 和 Blue 仍然是可变的(而它们不在枚举中).

Red, Green, and Blue are still mutable (whereas they are not in an enum).

枚举还提供了一些东西:

Enums also provide a few things:

1. 一组封闭的众所周知的值(以后不允许输入错误)，每个值都有...
2. 为每个成员提供一组各自的类似文字的类型，所有这些都提供...
3. 通过包含所有值的单个命名类型

例如，要使用命名空间之类的东西来实现它，您必须执行类似的操作

To get that with something like a namespace, for example, you have to do something like

export namespace Color
    export const Red = 1
    export type Red = typeof Red;

    export const Green = 2;
    export type Green = 2;

    export const Blue = 3;
    export type Blue = typeof Blue;
}
export type Color = Color.Red | Color.Blue | Color.Green

<小时>

您还注意到一些不幸的遗留行为，其中 TypeScript 允许从任何数值赋值给数字枚举.

---

What you're also noting is some unfortunate legacy behavior where TypeScript permits assignment from any numeric value to a numeric enum.

但是如果您使用的是字符串枚举，则不会出现这种行为.您还可以使用联合枚举启用其他功能，例如详尽检查:

But if you're using a string enum, you won't get that behavior. There are also other things like exhaustiveness checking that you can enable with union enums:

enum E {
  Hello = "hello",
  Beautiful = "beautiful",
  World = "world"
}

// if a type has not been exhaustively tested,
// TypeScript will issue an error when passing
// that value into this function
function assertNever(x: never) {
  throw new Error("Unexpected value " + x);
}

declare var x: E;
switch (x) {
  case E.Hello:
  case E.Beautiful:
  case E.World:
    // do stuff...
    break;
  default: assertNever(x);
}

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