javascript - 类型 'Observable<boolean | "“>' is not assignable to type ' 可观察< bool 值>” TS2322

Question

我正在从 NgRx 商店选择 @ngrx/store": "7.3.0" .

// typeof state.id == string

export const selectIsSomethingPresent = createSelector(selector, state => {
  // standard null check
  return state.id && state.id !== "12345";
});

我将它分配给一个 Observable

isSomethingPresent$ !: Observable<boolean>;

someMethod() {
  this.isSomethingPresent$ = this.store.select(selectIsSomethingPresent);
}

我收到此错误:

Type 'Observable<boolean | "">' is not assignable to type 'Observable<boolean>'.

为什么 typescript 会这样？

仅供引用return ("12345" && true)抛出同样的错误。

Answer 1

因为 state.id 类型是 string，空字符串 && true 将返回空字符串而不是 bool 值，因此您需要转换 state。 id 到 bool 值

return Boolean(state.id) && state.id !== "12345";