php - How to Alert the returned data of ajax?

Solution:

EDIT 2:

Alerting anything that PHP echos:

function get_data() {
    $.ajax({
        url: 'get_data.php?rand=' + Math.random(),
        type: 'GET'
        success: function(results) { 
            alert(results);
        }
    });
}
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EDIT 1:

If you want the errors to appear in an alert, do this:

for debugging ajax, you can check the xhr, status, and error like so:

function get_data() {
    $.ajax({
        url: 'get_data.php?rand=' + Math.random(),
        type: 'GET',
        error: function(xhr, status, error) {
            alert(status);
            alert(xhr.responseText);
        },
        success: function(results) { 
            /* clear old results, then display the new results */
            $("#divResults").empty().append(results);
        }
    });
}
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But this might not always display the full message, especially if the error message contains lots of data. it might end up going off the screen.

ORIGINAL ANSWER:

for debugging ajax, you can check the xhr, status, and error like so:

function get_data() {
    $.ajax({
        url: 'get_data.php?rand=' + Math.random(),
        type: 'GET',
        error: function(xhr, status, error) {
            /* clear old error message, then display the new php error message */
            $("#divErrorMessages").empty().append(status);
            $("#divErrorMessages").append(xhr.responseText);
        },
        success: function(results) { 
            /* clear the error message first */
            $("#divErrorMessages").empty();

            /* clear old results, then display the new results */
            $("#divResults").empty().append(results);
        }
    });
}
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In your HTML you should have the 2 divs

<div id="divResults"></div>
<div id="divErrorMessages"></div>
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Solution:

You can usesuccess handler in$.ajax call as diEcho wrote. Inside of this handler, you can decide by some flag whether your PHP operation succeeded or failed.

error handler of$.ajax is more likely for ajax call fail, than for status of requested operation.

Edit:

applying to example by diEcho:

$.ajax({
  url: "/post/post_url.php",
  type: "POST",
  data: parameters,
  success: function(data){
    alert('ajax call finished successfully');
    if (!data.insertedOk) {
      alert(data.message);
    } else {
      // insert succeeded
    }
  },
  error: function(){
    alert('ajax call failure');
    // this mean, /post/post_url.php calling failed (file not found etc...)
  }
});
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EDIT2:

in PHP you could use following

if ($queryExecutedSuccessfully) {
    $return['insertedOk'] = true;
    $return['message'] = 'Your success message';
} else {
    $return['insertedOk'] = false;
    $return['message'] = 'Error message when insert fails.';
}
echo json_encode($return);
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Solution:

try like this

$.ajax({
  url: "/post/post_url.php",
  type: "POST",
  data: parameters,
  success: function(){
    alert('success');
  },
  error: function(){
    alert('failure');
  }
});
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Reference

Solution:

Regarding the code of @diEcho, You also need to test insuccess: function() your returned answer with a status code (wrote by PHP).

In other hand, you can force the error in your PHP script by sending an "Error 500" header, that generate the "Fail" callback. But it's not a good way !

In your PHP:

if (true === $QueryHasFail) {
    header('HTTP/1.1 500 Internal Server Error'); // <--- Ajax Callback error: function() 
    echo "Oupss, somethink wrong!";
} else {
    echo "Yeah, great"; // <--- Ajax Callback success: function()
}
exit(0);
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More information here: http://www.rachaelarnold.com/dev/archive/trigger-ajax-error-event

Solution:

To alert what is echoed in your PHP, "data" is passed into the success function as the first parameter, which is then output in an alert in this example:

$.ajax({
  url: "/post/post_url.php",
  type: "POST",
  data: parameters,
  success: function(data){
    alert(data);
  },
  error: function(jqXHR, textStatus, errorThrown){
    alert('Failure: ' + textStatus + ". Error thrown: " + errorThrown);
  }
});
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Solution:

I know this is an old topic, but as i found it searching for something similar, i decided to add some information that could be useful for later searches.

I think a solution to this could be aproached by sending the appropriate header() or http_response_code($HTTP_ERROR_CODE); in your PHP Script, depending on the answers of your PHP Script. You can find related info in this posts:

How to make a ajax call to a php page a success or error?

How to send a server error response using php?

The function you select (header or http_response_code) it depends on the version of PHP you are using, it seems that http_response_code is available from PHP 5.4.

A workaround to avoid "PHP version crosscompiling" might be achieved by coding your own http_response_code in the case that testing for it existance results in failure, as is suggested in this other post of php.net:

http://php.net/manual/en/function.http-response-code.php

Latter, on your HTML/jQuery document, you can check your request.fail, request.done and request.always to retrieve the information provided by your PHP Script to use it at your convenience.

Hope this helps.