Combination Operators (Pipeable Operators)

RxJS's Combination Operators are powerful tools for combining multiple Observables to create new streams.

IMPORTANT

This page covers Pipeable Operators (form used in pipelines).

For Creation Functions (form that creates a new Observable from multiple Observables), see Chapter 3: Creation Functions.

Creation Functions vs Pipeable Operators

Functions related to combination are provided in two forms.

Creation Functions (explained in Chapter 3)

Receives multiple Observables as arguments and creates a new Observable.

import { concat, merge, combineLatest, zip, race, forkJoin } from 'rxjs';

// Use as Creation Function
const combined$ = concat(obs1$, obs2$, obs3$);
const merged$ = merge(source1$, source2$);

See Creation Functions for details.

Pipeable Operators (explained on this page)

Used in .pipe() for existing Observable.

import { concatWith, mergeWith, combineLatestWith } from 'rxjs';

// Use as Pipeable Operator
const result$ = source$.pipe(
  map(x => x * 2),
  concatWith(other$),
  filter(x => x > 10)
);

List of Pipeable Operators

◾ Operators Covered on This Page

Operator	Description
withLatestFrom	Combines the latest values of other streams according to the emission of the main Observable
mergeAll	Flatten Higher-order Observable in parallel
concatAll	Flatten Higher-order Observable sequentially
switchAll	Switch to the latest Higher-order Observable
exhaustAll	Ignore new Higher-order Observable during execution
combineLatestAll	Combine the latest values of all internal Observables
zipAll	Pair the corresponding values of each internal Observable

◾ Provided as Creation Functions

The following are mainly used as Creation Functions (see Chapter 3).

Function	Description	Pipeable Version
concat	Combine sequentially	concatWith (RxJS 7+)
merge	Combine in parallel	mergeWith (RxJS 7+)
combineLatest	Combine latest values	combineLatestWith (RxJS 7+)
zip	Pair corresponding values	zipWith (RxJS 7+)
race	Adopt the fastest stream	raceWith (RxJS 7+)
forkJoin	Wait for all to complete	(No Pipeable version)

For Those Who Want to Learn in a More Practical Way

For realistic scenario examples using combination operators, see Practical Use Cases for detailed information.