Ajax返回undefined

Question

I'm trying to upload a image to my server using a POST form and AJAX. But everytime I submit the form, my AJAX returns an undefined in my error box. This is the Ajax function I'm talking about:

$('.register_submit').click(function(e){
  e.preventDefault();

  $.ajax({
      type: "POST",
      url: "./functions/register.php",
      data: new FormData(this),
      contentType: false,
      processData: false,
       success : function(data){
          if (data.code == "200"){
              window.location.replace("./?page=home");
          } else {
              $(".display-error").html("<ul>"+data.msg+"</ul>");
              $(".display-error").css("display","block");
          }
      }
  });


});

and my form:

<form class="addCar_form" data-toggle="validator"  method="post" enctype="multipart/form-data" >
   <input type="file" class="form-control productimages" id="images" name="images[]" onchange="preview_images();" multiple/>
   <input type="submit" name="addCar_submit" value="Auto toevoegen" class="btn btn-default button addCar_submit">
</form>

Please do not mark this question as a duplicate, as I've been reading about ajax and it being asynchronous in other topics but I'm really not getting it from these answers. Anyone who sees what I'm doing wrong?

Answer 1

I think your server returns an error with a different status code. Therefor the success callback might not be called.

There are different callback available for $.ajax I think error is the one you need to check.

From the docs:

error callback option is invoked, if the request fails. It receives the jqXHR, a string indicating the error type, and an exception object if applicable. Some built-in errors will provide a string as the exception object: "abort", "timeout", "No Transport".

Try:

$('.register_submit').click(function (e) {
    e.preventDefault();

    $.ajax({
        type: "POST",
        url: "./functions/register.php",
        data: new FormData(this),
        contentType: false,
        processData: false,
        success: function (data) {
            if (data.code == "200") {
                window.location.replace("./?page=home");
            } else {
                $(".display-error").html("<ul>" + data.msg + "</ul>");
                $(".display-error").css("display", "block");
            }
        },
        error: function (xhr, ajaxOptions, thrownError) {
                    alert(xhr.status);
          alert(thrownError);
        }
    });
});