Understanding Why Your NestJS App Isn't Recognizing POST Requests from Fetch

Learn how to resolve issues with POST requests not being recognized in your NestJS application when using fetch in React.
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This video is based on the question https://stackoverflow.com/q/64786628/ asked by the user 'Alejandro' ( https://stackoverflow.com/u/5058488/ ) and on the answer https://stackoverflow.com/a/64786710/ provided by the user 'Emiel Zuurbier' ( https://stackoverflow.com/u/11619647/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Troubleshooting NestJS and Fetch: Why Your POST Requests Aren't Being Recognized

When developing a web application, you may find yourself facing challenges with data transmission between your front-end and back-end. One common issue developers encounter is when NestJS fails to recognize a POST request sent from a fetch call in React. If you’ve ever submitted a request and received an empty object in response, you’re not alone. Let’s dive into why this happens and how to fix it.

The Problem: Fetching Data Using POST Requests

You have a React application running on port 3000, which makes a POST request to your NestJS server running on port 8080. Here’s the relevant code snippet for your fetch request:

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

In your NestJS controller, the code that handles the incoming request looks like this:

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

You also have CORS enabled in your main application by using app.enableCors(). Despite getting the request to work in tools like Postman, when submitting from your React app, the server logs an empty object {}. What’s going wrong?

The Solution: Correctly Sending Data with Fetch

The root of the issue is in how you are sending data in your fetch request. In your original code, you used data to define the body of your request. Instead, the correct property to use is body. Additionally, you need to serialize your JavaScript object into JSON format. Here’s how to make the necessary changes to your fetch request:

Updated Fetch Request

Replace your existing fetch request with the following code:

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

Explanation of Changes

Use the body Property:

The fetch API uses the body property to send data in requests, not data. This is essential for the server to recognize the incoming payload correctly.

Convert Data to JSON:

JSON.stringify() is used to convert your JavaScript object into a JSON string. The server expects the body of the request to be in JSON format when you set the Content-Type to application/json.

CORS Configuration:

You already configured CORS, which ensures that your server can accept requests from a different origin. So, as long as your fetch request is correctly formatted, CORS should not be an issue.

Conclusion

Now that you know how to correctly format your fetch request, you should be able to send data to your NestJS server without encountering an empty object in the response.

Always remember to check the way data is sent in your fetch requests, especially the property to use and the format required by your server. By paying attention to these details, you can troubleshoot similar issues more effectively in your development process.

Happy coding!

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