JQuery $ .ajax请求json响应

Question

A JSON returned as response to this request is not recognized.

request = $.ajax({
        url: "form_handler.php",
        type: "post",
        dataType: "json",
        data: serializedData
});

The php code in form_handler.php which returns the response:

if ($success) {
    echo json_encode(array("success"=>"false"), JSON_PRETTY_PRINT); 
}
else
{
    echo json_encode(array("success"=>"true"), JSON_PRETTY_PRINT); 
}

And thus in:

request.done(data) 
{
    alert(data.success);     // error: cannot read property of 'success' of null 
}

Answer 1

I'm writing this as a wrap up of the answers and comments posted.

As @jetawe and @FelixKling pointed out, it would be a best practice to specify the Content-Type of the response, so add this at the head of the php script:

header('Content-Type: application/json');

@hindmost pointed out that the script is not failing since jqXHR.done() is actually called.

My guess is that there is a failure decoding the json object when $.ajax automatically decodes it (because of dataType: "json")

As @PaulRoub noticed, JSON_PRETTY_PRINT exists from the PHP version 5.4 so, if you have an older version of PHP, that constant wouldn't exists, throwing an error of level E_NOTICE and assuming the value null. Passing null (equal to 0) as a value json_encode would work anyway (assuming default behavior)

My second guess is that you have display_errors = 1 and error_reporting = E_ALL so PHP is printing out the error breaking the json.

I hope I guessed right!