Add delay to javascript method that returns promise

Delayed native promise

New promise that resolves with undefined

return new Promise(resolve =>
  setTimeout(resolve, 5000)
);

New promise that resolves with a value

return new Promise(resolve => 
  setTimeout(() => resolve(value), 5000)
);

Existing promise

return promise.then(value => 
  new Promise(resolve => 
    setTimeout(() => resolve(value), 5000)
  )
);

Delayed Bluebird promise

Bluebird promise library has better performance and convenient features that can be used out of the box to delay promise chains.

New promise that resolves with undefined

return Bluebird.delay(5000);

New promise that resolves with a value

return Bluebird.resolve(value).delay(5000);
// or
return Bluebird.delay(5000).return(value);

Existing promise

return bluebirdPromise.delay(5000);

Delayed promise with RxJS

RxJS is already used in Angular 2/4 projects and can be used to create or transform promises with RxJS operators and small overhead.

New promise that resolves with undefined

return Observable.of().delay(5000).toPromise();
// or
return Observable.interval(5000).first().toPromise();

New promise that resolves with a value

return Observable.of(value).delay(5000).toPromise();

Existing promise

return Observable.fromPromise(promise).delay(5000).toPromise();

Delayed result with RxJS 6

You can use the following code to delay values in RxJs 6 by n ms.

With no specific value (will emit 0)

return timer(n);

With a set value

return of(value).pipe(delay(n));

or

return timer(n).pipe(mapTo(value));

from a promise

return from(promise).pipe(delay(n));

to return a promise

put .toPromise() on any of the previous examples after the pipe.

return timer(n).toPromise();

return of(value).pipe(delay(n)).toPromise();

etc.