Скачать или смотреть Resolving the TypeError with rxjs Observables: Fixing Your Angular File Upload Function

Discover how to fix the `TypeError: Cannot read property 'subscribe' of undefined` when using `rxjs` observables with `switchMap` in your Angular file upload component.
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This video is based on the question https://stackoverflow.com/q/64585005/ asked by the user 'Christopher Jakob' ( https://stackoverflow.com/u/14358140/ ) and on the answer https://stackoverflow.com/a/64585090/ provided by the user 'elmetni' ( https://stackoverflow.com/u/2584297/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Resolving the TypeError with rxjs Observables: Fixing Your Angular File Upload Function

When working with Angular, you might encounter unexpected errors while dealing with rxjs observables. One common issue is facing a TypeError stating “Cannot read property 'subscribe' of undefined”. This can be particularly frustrating when your function runs without throwing an error but fails to send the expected requests to your server.

In this guide, we’ll delve into a specific case where this error occurs during a file upload process. Let’s break down the problem and explore how to fix it.

The Problem

In a particular Angular component, there’s a function designed to handle file uploads:

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

This function calls another function publicresourceuploadtos3, which is responsible for obtaining a presigned URL from the server and uploading the file. The original intent is to log the AJAX response once the file is successfully uploaded.

However, when you try to upload a file, you receive the following error:

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

The crucial aspect here is that the console log console.log('the service at least ran'); gets triggered, but the subsequent log console.log('did the call to the server'); does not.

Diagnosing the Issue

The error suggests that the function publicresourceuploadtos3 is not returning a valid observable. After taking a closer look at this function, the issue becomes clearer.

Original Issue in Code

The service function is implemented as follows:

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

Notice that there’s no return statement for the observable created by this.http.get(...). This leads to the function returning undefined, which explains why the subscriber fails and produces an error.

The Solution

To fix the issue, you need to add a return statement before the this.http.get(...) call. Here’s how the corrected function should look:

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

Key Changes Made

Adding the Return Statement: The key fix was simply adding a return statement so that the observable could be properly returned from the function.

Conclusion

Debugging issues with observables can be challenging, especially for those new to rxjs. By ensuring that each function properly returns the observables being created, you can avoid TypeError scenarios, like the one we encountered here. Remember, observables need to flow correctly through the functional chain to ensure that your components can subscribe to them successfully.

If you find yourself stuck with similar errors, take a moment to examine your services to ensure they are returning the expected observables. Happy coding!