Keywords: JSON | Chrome | SyntaxError | PHP | Content-Type | Debugging
Abstract: This article discusses the common Chrome error 'Uncaught SyntaxError: Unexpected token <' when handling JSON from PHP. It explains the primary causes, such as incorrect Content-Type headers in server responses, and provides solutions based on the best answer, including setting proper headers. Supplementary insights from other answers cover network console checks and file path issues, offering debugging tips to ensure cross-browser compatibility in JSON processing.
Understanding the Error
The error "Uncaught SyntaxError: Unexpected token <" in Google Chrome typically indicates that the JavaScript engine encountered an unexpected character, often the less-than sign (<), when parsing code. This commonly happens when the browser expects valid JSON data but instead receives HTML or other non-JSON content from the server.
Primary Cause and Solution
As highlighted in the best answer, a key cause is the incorrect Content-Type header in the server response. When PHP scripts output JSON data without setting the appropriate header, Chrome might interpret the response as JavaScript or default to HTML, leading to parsing errors.
To resolve this, ensure that your PHP file sets the correct Content-Type header. For example:
header("Content-Type: text/javascript; charset=utf-8");
This informs Chrome to treat the response as JavaScript, which can handle JSON parsing correctly. Alternatively, using application/json is recommended for strict JSON responses.
Supplementary Insights
Other answers provide additional context. Checking the Network console can reveal if the server is returning an error page starting with <. Issues with file paths, such as case sensitivity in URLs, can lead to 404 responses that return default HTML pages, causing the same error. Always validate server responses and ensure correct file references.
Best Practices
To prevent this error, follow these practices: always set Content-Type headers in server-side scripts, use tools like browser developer consoles to inspect network traffic, and test across different browsers to identify inconsistencies. Debugging with error logs and ensuring proper JSON encoding can mitigate common pitfalls.
Conclusion
The "Unexpected token <" error in Chrome is often a server-side issue related to content type mismatches. By setting appropriate headers and validating server responses, developers can ensure smooth JSON handling and cross-browser compatibility.