关于ajax调用的成功函数的一些精确性

Question

I'm creating a wordpress plugin and I use the wp_ajax_[your action] callback. In my code the php return nothing to the javascript (no echo, no return). If the php return no value, the 'data' in 'success: function(data)' is empty so why the 'click' trigger work?

the js:

$(document).one('click', '#publish', function (event) {

    event.preventDefault();

    jQuery.ajax({
        type:"post",
        url: ajaxurl,
        data: {action: 'save_img_data', imgUrlsArray: iUrlsArray, imgNamesArray: iNamesArray, pid: pl_vars.post_id}, 
        success: function(data) {
            $('#publish').trigger( "click" );
        }
    });
});

the php:

function lmg29_img_data() {

    $pid = $_POST['pid'];
    $iUrlsArray = $_POST['imgUrlsArray'];
    $iNamesArray = $_POST['imgNamesArray'];

    if (isset($iUrlsArray) and isset($iNamesArray)) {   
        update_post_meta( $pid, 'lg29_urls', $iUrlsArray  );
        update_post_meta( $pid, 'lg29_names', $iNamesArray  );
        die();
    }

}
add_action("wp_ajax_save_img_data", "lmg29_img_data");

as you can see there's no response:

Answer 1

The HTTP response code is 200, so it's considered a successful request. Actual data in the response is not required.

And, to be clear, functions in JS don't have mandatory arguments. There's no error if you call a function with arguments in its' declaration without any arguments provided.

A failure occurs if the response code is, for example, 400-something or 500-something. Like 404 or 503. https://en.wikipedia.org/wiki/List_of_HTTP_status_codes

To see how to set a response code read this:

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