Solving the TypeError: fetchedFile.blob is not a function in React Native

Discover effective solutions for the `TypeError: fetchedFile.blob is not a function` when working with blobs in React Native, especially with image data.
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This video is based on the question https://stackoverflow.com/q/72623333/ asked by the user 'user2465134' ( https://stackoverflow.com/u/2465134/ ) and on the answer https://stackoverflow.com/a/72624277/ provided by the user 'Fiston Emmanuel' ( https://stackoverflow.com/u/12431576/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Handling the TypeError: fetchedFile.blob is not a function in React Native

When working with React Native, especially while dealing with media and image files, developers sometimes encounter issues with blob data handling. One common error that users might face is the dreaded TypeError: fetchedFile.blob is not a function. In this guide, we will address the problem, why it occurs, and offer a solid solution to help you avoid running into this error in your own applications.

The Problem: Encountering the TypeError

In a typical scenario where you are attempting to retrieve an image file from the library using the launchImageLibrary function, you may expect to utilize the blob() method on a fetched file:

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

However, in some cases, especially when the data being processed is larger (like images), the blob() method may not be defined, resulting in the following error:

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

This issue can be especially prevalent when using certain environments or setups, such as an M1 Mac or a specific version of the iOS emulator.

Understanding the Cause

The underlying cause of this error is primarily due to how the React Native Fetch API is implemented. The fetch functionality, which is based on whatwg-fetch, can sometimes feel buggy, especially when handling large data like images. Thus, relying on fetchedFile.blob() may not yield consistent or reliable results across all platforms or devices.

A Reliable Solution: Using XMLHTTPRequest

To effectively work around this issue, an alternative approach is to use the XMLHttpRequest API, which provides better handling for large data types like blobs. Below, we will guide you through implementing this solution step-by-step.

Step-by-Step Implementation

Here’s how to modify your existing code to use XMLHttpRequest instead of the Fetch API:

1. Update the Function to Retrieve Image

Replace the existing getImageFromLibrary function with the following code:

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

Key Points to Note:

Error Handling: Always ensure you include error handling in your promises, as this helps manage unexpected scenarios gracefully.

Blob Type Management: By setting xhr.responseType to "blob", you can directly obtain the blob format instead of needing to convert it from a fetched response.

Conclusion

By switching from the default Fetch API to XMLHttpRequest, you can alleviate the issues related to blob handling in React Native apps. This method ensures a more stable and predictable interaction with large data types. If you continue to face challenges or have questions, feel free to reach out in the comments below.

Implement the proposed solutions in your own projects, and you'll likely find smoother sailing in your next mobile development endeavor!