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Learn how to effectively resolve AJAX issues in ASP.NET MVC when the status is 200 but ends in an error. Discover tips and best practices from debugging to returning JSON data successively.
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This video is based on the question https://stackoverflow.com/q/64389354/ asked by the user 'Mah' ( https://stackoverflow.com/u/12477597/ ) and on the answer https://stackoverflow.com/a/64389542/ provided by the user 'Brian Mains' ( https://stackoverflow.com/u/231716/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Troubleshooting AJAX Call Status 200 but Not Successful in ASP.NET MVC

In modern web applications, AJAX (Asynchronous JavaScript and XML) allows developers to communicate with servers without reloading the web pages. One common issue that can arise is when an AJAX call returns a status of 200 but is still not successful. This problem can leave developers baffled, especially when the expected data is not being processed as intended. Here, we'll outline potential solutions to this issue, specifically in the context of an ASP.NET MVC application.

The Problem Statement

You might be experiencing a situation where you make an AJAX call to your controller, and despite receiving an HTTP status of 200, your application still goes to the error section. This can be frustrating, especially when the response payload seems correct when accessed via a browser. So, what could be causing this behavior, and how can we resolve it?

Example Situation

To contextualize this, let’s consider the following code snippets:

Service Layer

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

Controller

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

JavaScript AJAX Call

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

The Error Encountered

When the AJAX call is made, the error logged states: TypeError: 'caller', 'callee', and 'arguments' properties may not be accessed on strict mode functions or the arguments objects for calls to them. This indicates that there could be a problem with the way the AJAX request is constructed or how the server is handling it.

Solution to the Problem

Here are step-by-step solutions to troubleshoot and resolve the issue effectively:

Step 1: Check the URL

Open your browser's Developer Tools and ensure the AJAX URL is correct. ASP.NET MVC applications commonly resolve URLs dynamically. Instead of hardcoding the URL as /App/Team/GetTeams, you should use the MVC URL Helper:

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

Step 2: Modify the Controller Response

Often, for AJAX calls, the controller should return a JSON result to work correctly with JavaScript. Modify your controller's action as follows:

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

Step 3: Understanding JSON Return

Returning JSON: Make sure your data is properly serialized to JSON. In ASP.NET MVC, using the Json() method helps ensure the data is converted into the right format.

AllowGet Flag: The JsonRequestBehavior.AllowGet parameter is important. It allows GET requests to return JSON results. Without this, any GET request returning JSON would be blocked by default, leading to an error.

Conclusion

Facing a situation where your AJAX call returns a status of 200 but fails can be frustrating, but it can often be resolved by ensuring that the URL is correctly constructed and the data is properly formatted and returned from the server. By following the steps outlined above, you can diagnose and fix this issue, giving users a smoother experience and helping your application function as expected.

If you have encountered similar issues or found additional solutions, feel free to share your insights in the comments below!