> For the complete documentation index, see [llms.txt](https://mm.ricky.moe/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://mm.ricky.moe/javascript/typescript/shi-yong/zi-mian-liang-lei-xing-shou-wei.md).

# 字面量类型守卫

当你在联合类型里使用字面量类型时，可以通过字面量类型守卫来区分：

```javascript
type Foo = {
  kind: 'foo'; // 字面量类型
  foo: number;
};

type Bar = {
  kind: 'bar'; // 字面量类型
  bar: number;
};

function doStuff(arg: Foo | Bar) {
  if (arg.kind === 'foo') {
    console.log(arg.foo); // ok
    console.log(arg.bar); // Error
  } else {
    console.log(arg.foo); // Error
    console.log(arg.bar); // ok
  }
}
```