Typescript: RXJS `distinctUntilChanged` 在严格模式下/第一个参数未定义时不起作用

以下代码不起作用：

let observable: Observable<{ key: number }> = of({ key: 123 });
observable.pipe(
    distinctUntilChanged(undefined, v => v.key)
);

尽管存在超载：

export function distinctUntilChanged<T, K>(
  comparator?: (previous: K, current: K) => boolean,
  keySelector: (value: T) => K = identity as (value: T) => K
): MonoTypeOperatorFunction<T>

这是为什么？

答案＃1

提供的示例不是 TypeScript 示例，因此 undefined 不能作为以下类型的第一个参数使用！请改为指定一个默认比较器并设置 keySelector！

类型定义：

import { MonoTypeOperatorFunction } from '../types';
export declare function distinctUntilChanged<T>(comparator?: (previous: T, current: T) => boolean): MonoTypeOperatorFunction<T>;
export declare function distinctUntilChanged<T, K>(comparator: (previous: K, current: K) => boolean, keySelector: (value: T) => K): MonoTypeOperatorFunction<T>;

代码：

import { of, distinctUntilChanged, Observable } from 'rxjs';
export interface TypeObj {
  updatedBy: string;
  data: Array<string>;
}
// A stream of updates to a given account
const accountUpdates$: Observable<TypeObj> = of(
  { updatedBy: 'blesh', data: [] },
  { updatedBy: 'blesh', data: [] },
  { updatedBy: 'ncjamieson', data: [] },
  { updatedBy: 'ncjamieson', data: [] },
  { updatedBy: 'blesh', data: [] }
);

// We only want the events where it changed hands
const changedHands$ = accountUpdates$.pipe(
  distinctUntilChanged<TypeObj, string>(
    (prev: string, curr: string): boolean => prev === curr,
    (update: TypeObj) => update?.updatedBy
  )
);

changedHands$.subscribe(console.log);

Stackblitz 演示

答案＃2

实际上，你误用了 distinctUntilChanged。像下面这样重构你的代码应该就可以了：

const observable: Observable<{ key: number }> = of({ key: 123 });
observable.pipe(
    distinctUntilChanged((prev, curr) => prev.key === curr.key)
);