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Discover an efficient way to parallel-fetch all pages from an external API using Angular 11, maximizing performance with `forkJoin`.
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Fetching All Pages in Parallel with Angular 11

When developing web applications, efficiently managing HTTP requests is crucial—especially when you're dealing with an external API that provides information in a paginated format. In this post, we will explore how to effectively fetch all pages in parallel using Angular 11.

The Problem

You encounter a situation where an external API returns a limited set of items along with pagination details. For instance, the API may return a result indicating that there are a total of 200 items, with 10 items per page. This means there are a total of 20 pages to retrieve.

To effectively utilize the API, you want to:

Make an initial call to ascertain the total number of pages.

Fetch the remaining pages in parallel to improve performance.

The Solution

To accomplish this in Angular 11, we can leverage RxJS operators like switchMap and forkJoin. Let’s break down the solution step-by-step:

Step 1: Trigger the First Request

The first step involves making a request to obtain the data for the first page. This response contains the total number of items and the pagination details needed for subsequent calls.

Step 2: Using switchMap

Next, you utilize the switchMap operator. The idea here is to switch from the first request to subsequent requests based on the total number of pages returned by the API.

Note: In Angular, HTTP requests complete after a single emission, so operators like concatMap, mergeMap, or exhaustMap can also be used interchangeably based on your use-case.

Step 3: Fetching Pages in Parallel

Depending on whether each page’s data is fetched through separate requests or all in a single request, you will use one of the two approaches:

3.1: Using forkJoin for Separate Requests

If each page is an individual request, you can utilize forkJoin to combine the requests and fetch them in parallel. Here’s how the code looks:

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

In the code example above:

We calculate the number of pages.

Create an array filled with the number of requests corresponding to each page.

forkJoin allows us to wait for all requests to complete before processing the results.

3.2: Handling a Single Request for All Pages

If your API supports fetching all pages in a single request, you can call the endpoint directly. This is typically more efficient. The modified code is:

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

Conclusion

By utilizing Angular 11’s powerful HTTP client in conjunction with RxJS operations, we can efficiently fetch data from APIs. Whether you need to make several requests in parallel or a single request for multiple pages, following the structured approach outlined above ensures that performance is optimized and the process is smooth.

By preparing for different scenarios (individual requests vs. single request), you can adapt your Angular application to leverage the best benefits of external data sources, enhancing user experience and application responsiveness.

Final Thoughts

Efficiently managing requests is a key skill for anyone developing modern web applications. As you grow more familiar with RxJS operators and Angular’s HTTP client, you’ll find even more ways to enhance your apps' performance—so keep experimenting!