04RxJS创建+合并类操作符

combineLatest

合并多个Observable，并返回每个Observable的最新值，必须要每个Observable都有发出值，combineLatest才能被订阅

import {combineLatest, timer} from 'rxjs'
const firstTimer = timer(0, 1000);
const secondTimer = timer(5000, 1000);
const combinedTimers = combineLatest(firstTimer, secondTimer)
combinedTimers.subscribe(value => console.log(value))

5秒后第二个流secondTimer发出第一个值，此时的第一个流firstTimer的值为4，所以combineLatest第一个订阅的值是[4,0]

concat

类似数组的concat，将每个Observable拼接起来，按顺序发出值

const timer$ = interval(1000).pipe(take(4));
//将无限的定时器发送值，通过take只取前成4个流
const sequence$ = range(1, 10);
//从1开始，发送10个数值
const result = concat(timer$, sequence$);
result.subscribe(x => console.log(x));

forkJoin

类似Promise.all，在每个Observables都完成后，合并它们发出的最后一个值

const observable = forkJoin([
  of(1, 2, 3, 4),
  Promise.resolve(8),
  timer(3000),
]);
observable.subscribe({
  next: value => console.log(value),
  complete: () => console.log('This is how it ends'),
})

3秒后合并发送流，打印[3,8,0]

merge

与cancat不同，merge是把值按发射的顺序，逐个进行融合

const click$ = fromEvent(document, 'click');
const timer$ = interval(1000);
const clicksOrTimer = merge(click$, timer$);
clicksOrTimer.subscribe(x => console.log(x))

单击事件和定时器的流穿插发送

• 设置最多合并几个Observable

最后一个参数设为2，表示不管合并了多少个流，merge最多也只能合并两个，与参数顺序无关

const timer1 = interval(1000).pipe(take(10), mapTo('a'));
const timer2 = interval(2000).pipe(take(6), mapTo('b'));
const timer3 = interval(500).pipe(take(10), mapTo('c'));
const merged = merge(timer1, timer2, timer3, 2);
merged.subscribe(x => console.log(x));

partition

将一个Observable流按条件分成两个

const observalbeValues = of(1, 2, 3, 4);
const [evens$, odds$] = partition(observalbeValue, value => value % 2=== 0);
odds.subscribe(x => console.log('odds', x))

//odds 1
//odds 3
//evens 2
//evens 4

race

类似Promise.race,在多个Observable中，持续推送最快发出值的那个

const obs1 = interval(1000).pipe(mapTo('fast one'))
const obs2 = interval(3000).pipe(mapTo('medium one'))
const obs3 = interval(5000).pipe(mapTo('slow one'))
race(obs1, obs2, obs3).subscribe(winner => console.log(winner))

fase one……

zip

合并多个Observable，会严格按照发射值的位置（索引），合并每个流发出的值

const obs1 = of<number>(1, 2);
const obs2 = of<string>('one', 'two')
zip(obs1, obs2).subscribe(x => console.log(x))
// [1, "one"]
// [2, "two"]