RxJS switchMap vs mergeMap vs concatMap

In this tutorial, you will learn about switchMap, mergeMap, and concatMap Operators.

switchMap, mergeMap, and concatMap are RxJS Operators.

switchMap Operator

switchMap Operator cancels the previous inner Observable and subscribes only to the latest one.

Note: switchMap Operator prevents outdated API responses.

Example:

this.searchControl.valueChanges.pipe(
  switchMap(value =>
    this.http.get(`/api/search?q=${value}`)
  )
);

Where to use switchMap Operator

You can use the switchMap Operator in many scenarios.

1. You can use on Search autocomplete.

2. You can use, when you need Live filtering.

3. You can use, when you need the Latest-only requests.

mergeMap Operator

mergeMap Operator executes all inner Observables in parallel, and it does not cancel previous requests.

Example:

from([1, 2, 3]).pipe(
  mergeMap(id =>
    this.http.get(`/api/user/${id}`)
  )
);

Where to use the mergeMap Operator

1. If you want parallel API calls.

2. If you want to upload multiple files and many more.

concatMap Operator

concatMap Operator executes inner Observables one at a time and waits for the previous to complete.

Example:

from([1, 2, 3]).pipe(
  concatMap(id =>
    this.http.get(`/api/order/${id}`)
  )
);

Where to use the concatMap Operator

1. If you want Sequential API calls.

2. If your program depends on previous operations.

3. If you want Queue-based processing.

switchMap vs mergeMap vs concatMap Comparison

Feature	switchMap	mergeMap	concatMap
Execution	Latest only	Parallel	Sequential
Cancels Previous	✔ Yes	❌ No	❌ No
Order Preserved	❌ No	❌ No	✔ Yes
Performance	Optimized	High but risky	Safe but slower
Best For	Search, live input	Parallel tasks	Sequential tasks

Interview Questions & Answers

Q 1: Which operator should be used for search?

Ans: switchMap Operator

Q 2: Which operator runs tasks in parallel?

Ans: mergeMap Operator

Q 3: Which operator runs tasks sequentially?

Ans: concatMap Operator

RxJS switchMap vs mergeMap vs concatMap – Interview Questions