Sending Data from Vanilla JS to .NET Core API

Learn how to send data from a vanilla JavaScript client to a .NET Core API efficiently. This guide covers practical code examples and common pitfalls.
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How to Send Data from Vanilla JavaScript to .NET Core API

Sending data from a client-side application to a server-side application can sometimes be tricky, especially when dealing with different data formats. If you're using vanilla JavaScript to send data to a .NET Core API but encountering issues, you're in the right place. In this guide, we'll walk through the common problems and provide a clear solution to efficiently send data from your JavaScript client to your backend API.

The Problem: Data Not Received by the Controller

You might be experiencing a common issue where the data prepared in your JavaScript client does not arrive as expected in your .NET Core API. To illustrate, let's consider the situation where you've set up an API endpoint to receive an error report but the data coming to your controller is null despite having defined the values on the client side.

Example Scenario

Let's assume you have this JavaScript snippet:

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

Despite the debugger showing populated values, the controller on the server-side receives nothing. The issue lies in how the data is being sent.

The Solution: Sending Data as FormData

The problem arises because you are trying to send an object containing FormData. According to the .NET Core API expectations, if you have specified [FromForm], your server expects the data to be sent in the form rather than as an object. Therefore, we need to append all of our data directly to the FormData object.

Step-by-Step Solution

Here’s how to correctly structure your JavaScript code for sending all necessary data via FormData:

Create a New FormData Object: Instead of creating an object and then putting it into FormData, you'll want to append each item directly.

Append All Necessary Form Fields: Ensure that all fields are added to the FormData instance.

Here's the corrected JavaScript code:

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

Key Adjustments Made:

FormData Structure: Each key-value pair is added directly to formData using append().

Correct Parameter in Axios Request: Send formData instead of an object that contains it.

Conclusion

By ensuring that all your data is appended to a single FormData instance, your .NET Core API should now be able to receive the data as expected. This approach avoids the common serialization issues that arise when mixing data formats. Remember to also test your endpoint and review any potential CORS issues if encountered.

With the right structure in your JavaScript code, integrating client-side applications with server-side APIs can become a lot more manageable. Happy coding!