Ajax request returns 200 OK, but an error event is fired instead of success

Understanding data responses and types

Avoid misinterpretations! If you're expecting HTML, not JSON, avoid dataType: 'json' as this will attempt to parse your HTML response as JSON and we all know how that goes (sad trombone sound). Instead, go for 'html':

dataType: 'html'
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Not so hard, is it?

Empty response or malformed JSON, who dis?

An empty response can still play nicely if returned as a null object or an empty JavaScript object {}. Like fitting a round peg into a square hole, malformed JSON won't parse, and you're left with undefined feelings. So, ensure your JSON is correctly formatted; your future self will thank you.

// Server-side pseudo-code
if (dataIsEmpty) {
  response.write('{}'); // Like a friendly ghost, an empty object doesn't cause any trouble!
}
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Content-Type header, our special secret handshake

The Content-Type header in your server response is like a special secret handshake 🤝. By setting this, you're telling the client how to handle the incoming data:

dataType: 'json'  // Client-side expectation
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Content-Type: application/json; charset=utf-8  // Server-side reality

It's a team effort!

Going nowhere without CORS

Working with cross-origin requests? Time to bring in the big guns! Make sure your server sends along the necessary CORS headers (Access-Control-Allow-Origin); otherwise your request will be stopped faster than trying to bring liquids through airport security. ☠️

Error handling like a pro

Props for making sure your request is perfect, but real champs are prepared for failure! Implement error callbacks to prevent potential issues:

error: function(xhr, status, error) {
  console.error("Received an AJAX error status:" + status);
}
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Debug smarter, not harder

Side-step those obstacles by debugging Ajax calls and responses. The network tab in your browser's inspect tool is your secret weapon here 🔎.

Keeping data compatibility at 100%

For more flexible Ajax requests, set your dataType as 'text json'. The response will be treated first as text, then parsed as JSON:

$.ajax({
  url: "your-enpoint",
  dataType: "text json", // Response first treated as text, then parsed as json
  // ...
});
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Parsing JSON right

Throwing a party on the ASP.NET side? Don't forget to invite JavaScriptSerializer for correct JSON serialization. This advice holds for other server-side languages too — the right method of serialization is your BFF here.