[RxJS] AsyncSubject: representing a computation that yields a final value-优快云博客

本文详细介绍了RxJS中的AsyncSubject，一种特殊的Subject类型，它只在序列完成时才重播最后一个值。通过示例代码展示了AsyncSubject与其他Subject类型的差异，并提供了具体的使用场景。

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This lesson will teach you about AsyncSubject, another type of Subject with some replaying logic inside. We will also look at some use cases for this peculiar RxJS subject variant.

AsyncSubject:

Emit last value only when sequence completed.

BehaviorSubject:

Replay onces, only before compleation.

ReplaySubject:

Replay many, before of after compleation.

var subject = new Rx.AsyncSubject();

// Subject
// ReplaySubject: replays many, before or after completion
// BehaviorSubject: replays one, only before completion
// AsyncSubject: replays one, only if completed

var observerA = {
  next: function (x) { console.log('A next ' + x); },
  error: function (err) { console.log('A error ' + err); },
  complete: function () { console.log('A done'); },
};

subject.subscribe(observerA);
console.log('observerA subscribed');

var observerB = {
  next: function (x) { console.log('B next ' + x); },
  error: function (err) { console.log('B error ' + err); },
  complete: function () { console.log('B done'); },
};

setTimeout(() => subject.next(1), 100);
setTimeout(() => subject.next(2), 200);
setTimeout(() => subject.next(3), 300);
setTimeout(() => subject.complete(), 350);

/*
----1---2---3--|       
  .............3|
                   3|
*/

setTimeout(function () {
  subject.subscribe(observerB);
  console.log('observerB subscribed');
}, 400);

/*
"observerA subscribed"
"A next 3"
"A done"
"B next 3"
"B done"
"observerB subscribed"
*/

转载于:https://www.cnblogs.com/Answer1215/p/5977464.html