Question

Is there a way to let php error messages show up in a facebook canvas app for my own debugging purposes, or does facebook truncate errors before sending output to the browser?

A related question is whether or not php error messages normally appear in the browser window in the first place.

Answer 1

First thing i’d recommend you is to use “Firebug” for firefox, it helps a lot to debug
while you’re working on your application. Another thing is the built-in facebook API Exception (PHP SDK) Try-Catch:

try
{
    // Your Graph API Calls Ex: $userInfo = $facebook->api("/me","GET");   
}
catch (FacebookApiException $e) {
// After you're done debugging, comment out the below lines
       $result = $e->getResult();
       echo "<pre>";
       print_r($result);
       echo "</pre>";
}

If you don’t know what is Exception, then check out this link: PHP Exception Handling

Also this might help you as well: PHP Error Handling or set_error_handler