取（1）与FirstValue，从可观察到的Value。

发布于 2025-01-20 19:47:49 字数 864 浏览 6 评论 0原文

在我的项目中，我使用cimakiorSubject作为数据存储来存储我的应用程序的状态。

我只需要当前值，该值当前在evaryubjectubject存储中，并且不需要订阅可以通过行为主题发出的未来值。

我发现如何做到这一点的实现很少：使用管道（拿（1）），firstValuefrom和.value。

所有人都以相同的方式工作并阅读行为主题存储中的当前值吗？它们之间有什么区别（如果有）？

private myStore$: BehaviorSubject<boolean> = new BehaviorSubject<boolean>(false);

// reading only one current value using take(1):
this.myStore$.pipe(take(1))
    .subscribe(value => console.log('current value = ', value));

// reading only one current value using firstValueFrom:
const value = await firstValueFrom(this.myStore$);
console.log('current value = ', value);

// reading only one current value using this.myStore$.value:
const value = this.myStore$.value;
console.log('current value = ', value);

原文

In my project, I use BehaviorSubjects as data stores to store the state of my application.

I need only the current value that is currently held in the BehaviorSubject store, and don't need to subscribe to future values that can be emitted through the behavior subject.

I found few implementations of how to do this: using pipe(take(1)), firstValueFrom and .value.

Do all work the same way and read the current value in the BehaviorSubject store?
What are the differences between them, if any?

private myStore$: BehaviorSubject<boolean> = new BehaviorSubject<boolean>(false);

// reading only one current value using take(1):
this.myStore$.pipe(take(1))
    .subscribe(value => console.log('current value = ', value));

// reading only one current value using firstValueFrom:
const value = await firstValueFrom(this.myStore$);
console.log('current value = ', value);

// reading only one current value using this.myStore$.value:
const value = this.myStore$.value;
console.log('current value = ', value);

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凡尘雨 2025-01-27 19:47:49

基本上使用 take(1) 或 firstValueFrom 是相同的，因为它们异步访问值：

myStore$.pipe(
  take(1)
).subscribe(value => {...});

firstValueFrom 将 Observable 转换为 Promise，因此您可以使用 < code>async/await：

const value = await firstValueFrom(myStore$);

使用BehaviorSubject.value同步访问其值一般是不推荐。如果 BehaviorSubject 错误或取消订阅，它可能会出现意外行为：

import { BehaviorSubject } from 'rxjs';

const subject1 = new BehaviorSubject(1);
console.log(subject1.value);
subject1.error(new Error('broken'));
try {
  console.log(subject1.value);
} catch (e) {
  console.error(e);
}

const subject2 = new BehaviorSubject(2);
console.log(subject2.value);
subject2.unsubscribe();
try {
  console.log(subject2.value);
} catch (e) {
  console.error(e);
}

实时演示：https://stackblitz.com/edit/rxjs-npalak?devtoolsheight=60

Basically using take(1) or firstValueFrom is the same because they access the value asynchronously:

myStore$.pipe(
  take(1)
).subscribe(value => {...});

firstValueFrom turns Observable into a Promise so you can use async/await:

const value = await firstValueFrom(myStore$);

Using BehaviorSubject.value to synchronously access its value is in general not recommended. It might behave unexpectedly if BehaviorSubject errors or when it's unsubscribed:

import { BehaviorSubject } from 'rxjs';

const subject1 = new BehaviorSubject(1);
console.log(subject1.value);
subject1.error(new Error('broken'));
try {
  console.log(subject1.value);
} catch (e) {
  console.error(e);
}

const subject2 = new BehaviorSubject(2);
console.log(subject2.value);
subject2.unsubscribe();
try {
  console.log(subject2.value);
} catch (e) {
  console.error(e);
}

Live demo: https://stackblitz.com/edit/rxjs-npalak?devtoolsheight=60

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