如何在 TypeScript 中使用带枚举的 Switch 语句

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在 TypeScript 中使用带枚举的 Switch 语句

How to use a Switch statement with Enums in TypeScript

要将 switch 语句与枚举一起使用：

  1. 创建一个将枚举值作为参数的可重用函数。
  2. 使用 switch 语句并打开提供的值。
  3. 从每个分支返回一个特定的值。
索引.ts
enum Sizes {
  Small,
  Medium,
}

function getSize(size: Sizes) {
  switch (size) {
    case Sizes.Small:
      console.log('small');
      return 'S';
    case Sizes.Medium:
      console.log('medium');
      return 'M';

    default:
      throw new Error(`Non-existent size in switch: ${size}`);
  }
}

console.log(getSize(Sizes.Small)); // 👉️ "S"
console.log(getSize(Sizes.Medium)); // 👉️ "M"

我们创建了一个可重用的函数，它将枚举值作为参数，在返回其他内容之前打开枚举值。

默认情况是一个实现问题。在示例中，我们抛出一个错误以指示发生了意外状态 – 传入的值不存在于枚举中。

If you have a
numeric enum
and you try to use a switch statement directly, you might get an error that
“Type X is not compatible to type Y”.

In this scenario, you can convert the enum value to a number when switching on
it.

index.ts
enum Sizes {
  Small,
  Medium,
}

switch (Number(Sizes.Small)) {
  case Sizes.Small:
    console.log('size is S');
    break;
  case Sizes.Medium:
    console.log('size is M');
    break;

  default:
    console.log(`non-existent size: ${Sizes.Small}`);
    break;
}

Had we not converted the enum value to a number when switching on it, we would
get an error that the two types are not compatible.

Make sure to always use the break keyword to avoid a fallthrough switch, which
could run multiple code blocks.

If you’re in a function, you will most likely be using return instead of
break.

If you are getting a similar error when working with string enums, you can
convert the value to a string in the switch statement.

index.ts
enum Sizes {
  Small = 'S',
  Medium = 'M',
}

switch (String(Sizes.Small)) {
  case Sizes.Small:
    console.log('size is S');
    break;
  case Sizes.Medium:
    console.log('size is M');
    break;

  default:
    console.log(`non-existent size: ${Sizes.Small}`);
    break;
}

如果您运行上面示例中的代码，size is S消息将记录到控制台。

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