Скачать или смотреть How to Make an HTTP Request with Authorization Header from a Readable Store in Svelte

Learn how to manage HTTP requests efficiently in Svelte by using a readable store for authentication headers, ensuring requests only trigger once the token is set.
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This video is based on the question https://stackoverflow.com/q/70303452/ asked by the user 'disciplus' ( https://stackoverflow.com/u/3267445/ ) and on the answer https://stackoverflow.com/a/70303834/ provided by the user 'Thomas Hennes' ( https://stackoverflow.com/u/5438616/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Managing HTTP Requests in Svelte with Authorization Headers

When developing applications that involve APIs, managing authentication tokens is a crucial aspect. In a Svelte application, you may want to make an HTTP request using the Authorization header populated with a token obtained through a previous request. If not configured correctly, you might find your request triggering unexpectedly—in particular, when the token store is initially empty.

In this guide, we'll dive into a common problem faced by Svelte developers regarding managing an Authorization token from a store, and provide a clear, step-by-step solution to ensure your HTTP requests behave as expected.

The Problem

When initializing your readable store, it starts with an empty string. Thus, any component that subscribes to this store receives the initial value immediately. This results in your HTTP request being made twice:

The first request executes with an empty string for the token.

The second request executes when the store updates with the new token value.

To prevent this dual request scenario, you need a strategy to effectively check if the token is present before making the HTTP request.

The Solution: Implementing Conditional Logic

To resolve this issue, follow the steps outlined below:

Step 1: Update the Subscription Logic

Modify the subscribe method for your token store to check if the token is present before proceeding with the request. Here's how you can implement it:

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

In this code snippet:

We're checking the value t (the token) provided by the store.

If t is truthy (meaning a valid token exists), we execute listFinancialInstitutions() with that token.

If t is falsy (an empty string or not yet set), we set financialsPromise to undefined, preventing any unwanted requests.

Step 2: Conditional Rendering of the Promise

Next, we want to conditionally render the promise based on whether it exists. This provides a better user experience and avoids rendering issues when the token is not available yet. Wrap the rendering logic in an if block:

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

In this modified rendering block:

The promise contents are only rendered if it exists.

This ensures that users don't see a loading state or an error when the token isn't available.

Conclusion

Managing HTTP requests in a Svelte application, particularly when dealing with authorization tokens, requires careful control over the store's selected values. By implementing a check for the token's existence before making requests and conditionally rendering promise outputs, you can significantly optimize application performance and enhance user experience.

By following these steps, you’ll ensure your listFinancialInstitutions() method is called only when there is a valid token, preventing redundant requests and improving your application's behavior!

Now that you’re armed with this knowledge, you can dive deeper into creating efficient and responsive applications using Svelte.