Subject는 옵저버들 간에 단일 실행 경로를 공유하는 특별한 유형의 옵저버블입니다.
사람들로 가득 찬 방에서 마이크를 들고 말하는 단 한 명의 사람으로 생각할 수 있습니다. 그들의 메시지 (the subject) 는 수많은 (multicast) 사람들에게 (the observers) 동시에 전달됩니다. 바로 멀티캐스팅 의 개념입니다. 일반적인 옵저버블은 1대 1의 대화라고 생각할 수 있습니다.
Copy /*
s1 n(r) n(x) s2 n(j) c n(s)
Subject
s1 ^-----r------x--------------j------|----------
s2 ---------------------^------j------|----------
AsyncSubject
s1 ^----------------------------------j|---------
s2 ---------------------^-------------j|---------
BehaviorSubject
s1 ^a----r------x--------------j------|----------
s2 ---------------------^x-----j------|----------
ReplaySubject
s1 ^-----r------x--------------j------|----------
s2 ---------------------^r-x---j------|----------
*/
// RxJS v6+
import { Subject, AsyncSubject, BehaviorSubject, ReplaySubject } from 'rxjs';
const subject = new Subject();
const asyncSubject = new AsyncSubject();
const behaviorSubject = new BehaviorSubject('a');
const replaySubject = new ReplaySubject(2);
const subjects = [subject, asyncSubject, behaviorSubject, replaySubject];
const log = subjectType => e => console.log(`${subjectType}: ${e}`);
console.log('SUBSCRIBE 1');
subject.subscribe(log('s1 subject'));
asyncSubject.subscribe(log('s1 asyncSubject'));
behaviorSubject.subscribe(log('s1 behaviorSubject'));
replaySubject.subscribe(log('s1 replaySubject'));
console.log('\nNEXT(r)');
subjects.forEach(o => o.next('r'));
console.log('\nNEXT(x)');
subjects.forEach(o => o.next('x'));
console.log('\nSUBSCRIBE 2');
subject.subscribe(log('s2 subject'));
asyncSubject.subscribe(log('s2 asyncSubject'));
behaviorSubject.subscribe(log('s2 behaviorSubject'));
replaySubject.subscribe(log('s2 replaySubject'));
console.log('\nNEXT(j)');
subjects.forEach(o => o.next('j'));
console.log('\nCOMPLETE');
subjects.forEach(o => o.complete());
console.log('\nNEXT(s)');
subjects.forEach(o => o.next('s'));
/*
OUTPUT:
SUBSCRIBE 1
s1 behaviorSubject: a
NEXT(r)
s1 subject: r
s1 behaviorSubject: r
s1 replaySubject: r
NEXT(x)
s1 subject: x
s1 behaviorSubject: x
s1 replaySubject: x
SUBSCRIBE 2
s2 behaviorSubject: x
s2 replaySubject: r
s2 replaySubject: x
NEXT(j)
s1 subject: j
s2 subject: j
s1 behaviorSubject: j
s2 behaviorSubject: j
s1 replaySubject: j
s2 replaySubject: j
COMPLETE
s1 asyncSubject: j
s2 asyncSubject: j
NEXT(s)
*/ 