Save Indicator

This recipe demonstrates the creation of a google docs-esque save indicator with RxJS.

Ultimate RxJS

Example Code

( StackBlitz )

Save Indicator
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$.pipe(
debounceTime(200),
map(e => e.target.value),
distinctUntilChanged(),
share()
);
const savesInProgress$ = inputToSave$.pipe(
mapTo(of('Saving')),
tap(_ => savesInProgress++)
);
const savesCompleted$ = inputToSave$.pipe(
mergeMap(saveChanges),
tap(_ => 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: ${format(Date.now(), 'MM/DD/YYYY hh:mm')}`))
)
)
);
merge(savesInProgress$, 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;
});