combineLatestAll - Combine Latest Values of All Internal Observables

The combineLatestAll operator takes a Higher-order Observable (Observable of Observables), once all internal Observables have fired at least once, combines their latest values and outputs them as an array.

🔰 Basic Syntax and Usage

import { interval, of } from 'rxjs';
import { combineLatestAll, take } from 'rxjs';

// Higher-order Observable with three internal Observables
const higherOrder$ = of(
  interval(1000).pipe(take(3)), // 0, 1, 2
  interval(500).pipe(take(4)),  // 0, 1, 2, 3
  interval(2000).pipe(take(2))  // 0, 1
);

// Combine latest values once all internal Observables have fired at least once
higherOrder$
  .pipe(combineLatestAll())
  .subscribe(values => console.log(values));

// Output:
// [1, 3, 0] ← When all have fired at least once (after 2 seconds)
// [2, 3, 0] ← 1st Observable fires 2 (after 3 seconds)
// [2, 3, 1] ← 3rd Observable fires 1 (after 4 seconds)

• Collects internal Observables when Higher-order Observable completes
• Once all internal Observables have fired at least once, starts combining
• Whenever any internal Observable emits a value, combines all latest values and outputs

🌐 RxJS Official Documentation - combineLatestAll

💡 Typical Usage Patterns

• Combine latest results of multiple API calls
• Synchronize latest values of multiple form inputs
• Integrate multiple real-time data sources

🔄 Related Creation Function

While combineLatestAll is primarily used for flattening Higher-order Observables, use the Creation Function combineLatest for normal multi-Observable combinations.

import { combineLatest, interval } from 'rxjs';

// Creation Function version (more common usage)
const combined$ = combineLatest([
  interval(1000),
  interval(500),
  interval(2000)
]);

combined$.subscribe(console.log);

See Chapter 3: Creation Functions - combineLatest.

🔄 Related Operators

Operator	Description
mergeAll	Subscribe to all internal Observables in parallel
concatAll	Subscribe to internal Observables in order
switchAll	Switch to new internal Observable
zipAll	Pair values in corresponding order from each internal Observable

⚠️ Important Notes

Higher-order Observable Must Complete

combineLatestAll waits to collect internal Observables until the Higher-order Observable (outer Observable) completes.

❌ Nothing output because Higher-order Observable doesn't complete

interval(1000).pipe(
  map(() => of(1, 2, 3)),
  combineLatestAll()
).subscribe(console.log); // Nothing output

✅ Complete with take

interval(1000).pipe(
  take(3), // Complete after 3
  map(() => of(1, 2, 3)),
  combineLatestAll()
).subscribe(console.log);

All Internal Observables Must Fire at Least Once

No values will be output until all internal Observables have fired at least once.

import { of, NEVER } from 'rxjs';
import { combineLatestAll } from 'rxjs';

// Nothing output if even one internal Observable never fires
of(
  of(1, 2, 3),
  NEVER // Never fires
).pipe(
  combineLatestAll()
).subscribe(console.log); // Nothing output

Memory Usage

Note memory usage if there are many internal Observables, since latest values of all internal Observables are kept in memory.