combination

forkJoin

Waits for all provided Observables to complete, then emits an array of their last values — like Promise.all() for Observables.

Signature

forkJoin<T extends readonly unknown[]>(sources: [...ObservableInputTuple<T>]): Observable<T>

Marble Diagram

a$:     --1--2--3|
b$:     ----A--B|
forkJoin([a$, b$])
result: --------[3, B]|
(emits only when ALL complete)

Example

import { forkJoin } from 'rxjs'
import { ajax } from 'rxjs/ajax'

forkJoin({
  user:    ajax.getJSON('/api/user/1'),
  posts:   ajax.getJSON('/api/posts?userId=1'),
  friends: ajax.getJSON('/api/friends?userId=1')
}).subscribe(({ user, posts, friends }) => {
  renderProfile(user, posts, friends)
})

Common Use Cases

Load all data needed for a page in parallel before rendering
Run multiple independent API calls and wait for all to finish
Batch operations where you need every result before proceeding

Flow Diagram