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Learn how to manage multiple subscriptions in Angular using TypeScript and execute functions after both complete with `forkJoin`.
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Execute Function After Two Subscriptions Return - A Guide for TypeScript in Angular

When working with services in Angular, it’s common to encounter scenarios where you need to fetch data from multiple endpoints. This can become complex, especially when you want to ensure that a certain piece of code runs only after both data calls have successfully completed. If you've ever found yourself juggling multiple subscriptions and wanting to execute code after all of them finish, this guide is for you!

The Problem at Hand

Imagine you have a case where you need to fetch user data alongside their roles. You may have written code similar to the following in your ngOnInit method:

[[See Video to Reveal this Text or Code Snippet]]

In this code, you have two independent subscriptions:

One that retrieves user data based on an ID.

Another that retrieves all roles available.

However, with this approach, if you want to perform an operation that depends on both user and roles, you will run into issues since the code will be executed before either subscription completes. This is where the forkJoin operator comes in handy!

The Solution: Using forkJoin

To address the issue of managing multiple subscriptions and coordinating their results, you can utilize the forkJoin operator from RxJS. This operator allows you to wait for all observables (in this case, your data fetching functions) to complete and then execute a single subscription.

Step-by-step Implementation

Import forkJoin: Ensure that you import forkJoin from RxJS in your component.

Refactor Your Code: Replace your existing subscriptions with a forkJoin function call to combine the two observables.

Here’s how you can implement this in your Angular code:

[[See Video to Reveal this Text or Code Snippet]]

Explanation of the Code

forkJoin: This operator takes an object where you can name each observable. Here, we labeled them as user and roles.

subscribe: Once all of the observables complete, you will receive a combined result object containing the outputs of both calls.

results.user provides you with the user data.

results.roles gives you the roles data.

Further Execution: After accessing both pieces of data, you can now proceed with any additional logic safely, knowing that both APIs have returned their results.

Benefits of Using forkJoin

Clarity and Clean Code: By using forkJoin, your code becomes cleaner and easier to understand.

Reduced Complexity: You avoid the nested subscription pattern, which can lead to “callback hell” and make things harder to test and maintain.

Synchronization: Ensures that you only run the dependent logic when both API calls return their responses.

Conclusion

Managing multiple subscriptions can be challenging, but with forkJoin, you can simplify the process significantly in your Angular applications. By using this method, you ensure that your functions execute only when all necessary data is available, leading to cleaner, more efficient code.

Now you're all set to implement this in your own projects! Happy coding!