Understanding ForkJoin and MergeMap in Angular ?

Angular is a powerful framework for building single-page applications, and it provides a variety of operators to handle asynchronous operations and manage data flow. Two of the most useful operators in Angular’s RxJS-based system are forkJoin and mergeMap. These operators can be used to manage multiple observables and compose asynchronous workflows effectively.

In this blog post, we’ll take a deeper dive into these two concepts, understand how they work, and learn how and when to use them in an Angular application.

What is ForkJoin in Angular?

forkJoin is an operator in RxJS that allows you to combine multiple observables and wait for all of them to complete before emitting a single array of results. It's useful when you need to execute multiple HTTP requests simultaneously and gather the results once they have all completed.

Key Points about forkJoin:

• It takes an array (or an object) of observables as input.
• It waits for all the observables to complete, then emits an array of their last emitted values.
• If any observable errors, the entire forkJoin sequence will fail, and no values will be emitted.

Example Use Case