Скачать или смотреть Troubleshooting Your JSON POST Request in React.js

Learn how to effectively troubleshoot and solve issues with `JSON` POST requests in React.js, including an important insight on using FileReader asynchronously.
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This video is based on the question https://stackoverflow.com/q/76571279/ asked by the user 'kirvel' ( https://stackoverflow.com/u/13136530/ ) and on the answer https://stackoverflow.com/a/76571416/ provided by the user 'mbojko' ( https://stackoverflow.com/u/7194268/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Troubleshooting Your JSON POST Request in React.js: A Comprehensive Guide

Introduction

Are you struggling with JSON POST requests in your React.js application? If so, you’re not alone! Many developers encounter issues when trying to send data from their frontend to a backend server, particularly when working with file uploads. In this guide, we will dive into a common problem related to sending a base64 encoded PDF file using a fetch request and provide a step-by-step solution.

Understanding the Problem

When you attempt to send a JSON POST request using a file reader in your React.js app, you may receive an error like this:

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This typically happens when the request is not structured correctly or the data is not ready to be sent when the fetch request is made.

Examining the Code

The code snippet you are trying to execute is as follows:

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Step-by-Step Solution

1. Understanding Asynchronous Behavior

The key issue here is that the FileReader works asynchronously. When you call reader.readAsBinaryString(selectedFile);, the reading process begins, but the next line that tries to send the fetch request is executed immediately, before the file is actually read.

2. Move Fetch inside OnLoad

To properly handle this, you need to ensure that your fetch call occurs only after the file has been read. This can be done by moving the fetch request into the onload callback of the FileReader:

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3. Cleaning Up the Code

Additionally, it’s good practice to avoid mixing await with .then(). Choose one style of handling promises to improve the readability of your code.

Conclusion

By making these adjustments, your JSON POST request in React.js should work smoothly and resolve the 500 error you encountered. Always remember that asynchronous functions require careful handling, especially when file processing is involved. If you follow these guidelines, you will enhance the reliability of your data transmission capabilities in your applications.

Thank you for reading, and happy coding!