[RxJS] SwitchAll() - switch between two observables display always latest value
2021/9/16 6:06:14
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Converts a higher-order Observable into a first-order Observable producing values only from the most recent observable sequence
import './style.css'; import { fromEvent, of, merge, empty, concat, defer } from 'rxjs'; import { delay, map, mergeMap, tap, debounceTime, distinctUntilChanged, mapTo, filter, share, switchAll } from 'rxjs/operators'; import { format } from 'date-fns'; // track in progress saves let savesInProgress = 0; // references const input = document.getElementById('note-input'); const saveIndicator = document.querySelector('.save-indicator'); // streams const keyup$ = fromEvent(input, 'keyup'); // fake save request const saveChanges = value => { return of(value).pipe(delay(1500)); }; /** * Trigger a save when the user stops typing for 200ms * After new data has been successfully saved, so a saved * and last updated indicator. */ const inputToSave$ = keyup$.pipe( debounceTime(200), // @ts-ignore map(e => e.target.value), distinctUntilChanged(), share() ); const savesInProgress$ = inputToSave$.pipe( mapTo(of('Saving')), tap(_ => { savesInProgress++; console.log('savesInProgress++', savesInProgress); }) ); const savesCompleted$ = inputToSave$.pipe( mergeMap(saveChanges), tap(_ => { savesInProgress--; console.log('savesInProgress++', savesInProgress); }), // ignore if additional saves are in progress filter(_ => !savesInProgress), mapTo( concat( // display saved for 2s of('Saved!'), empty().pipe(delay(2000)), // then last updated time, defer for proper time defer(() => of(`Last updated: ${format(Date.now(), 'MM/DD/YYYY hh:mm:ss')}`) ) ) ) ); merge(savesInProgress$, savesCompleted$) .pipe( /* If new save comes in when our completion observable is running, we want to switch to it for a status update. */ switchAll() ) .subscribe(status => { saveIndicator.innerHTML = status; });
<iframe height="240" src="https://stackblitz.com/edit/rxjs-3txbvy?file=index.ts" style="width: 100%; height: 500px" width="320"></iframe>
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