rxjs - 过滤 BehaviorSubject

Question

我有一个 BehaviorSubject我希望能够filter ，但要保持新订阅者在订阅时始终获得一个值的行为主题式质量，即使最后发出的值被过滤掉。有没有一种简洁的方法可以使用 rxjs 的内置函数来做到这一点？例如:

const isEven = (n) => n % 2 === 0;
const source = new BehaviorSubject(1);
const stream = source.pipe(filter(isEven));
stream.subscribe((n) => console.log(n)); // <- I want this to print `1`
source.next(2); // prints `2`; that's good
source.next(3); // does not print anything; that's good

我已经编写了自己的实现，但如果它很容易，我更喜欢使用现有运算符的更简单的解决方案。

Answer 1

只需使用第二个 BehaviorSubject

const { BehaviorSubject } = rxjs;
const { filter} = rxjs.operators;

const isEven = (n) => n % 2 === 0;
const source = new BehaviorSubject(1);
const stream = new BehaviorSubject(source.getValue());

source.pipe(filter(isEven)).subscribe(stream);

stream.subscribe(val => { console.log(val); });
source.next(2);
source.next(3);

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