Why Am I Getting a \'Uncaught SyntaxError: Unexpected token :\' Error When Parsing AJAX JSON Responses in Chrome?

Uncaught SyntaxError: Parsing JSON Returned from AJAX Call

When parsing JSON returned from an AJAX call in MooTools, it's possible to encounter a "Uncaught SyntaxError: Unexpected token :" error in Chrome. This error arises when the response contains HTML content instead of valid JSON data.

The JSON response in your code:

{"votes":47,"totalvotes":90}

appears to be correct. However, Chrome's developer's console indicates an error with an unexpected token. This discrepancy suggests that something in the response might have caused the parsing error.

Cause of the Error

The error occurs due to HTML content being returned by the server. Chrome expects a valid JSON response, but the server is likely sending a complete HTML document. The top line of the HTML document, typically , triggers the syntax error when MooTools attempts to parse the JSON.

Solution

To resolve the error, ensure that the server responds with valid JSON data. Check for any console errors or logs on the server side that may indicate issues with the JSON encoding or content.

Here are some steps to debug the issue:

1. Check the network tab in Chrome's developer's console to confirm that the AJAX request is indeed returning an HTML document.
2. Inspect the response body to determine if it contains the line.
3. Ensure that the content type of the response is set to application/json to indicate that it contains JSON data.
4. Fix the server-side code to generate a valid JSON response without any HTML content.

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