Pete Pete - 5 months ago 46x
PHP Question

Jquery/Ajax Form Submission (enctype="multipart/form-data" ). Why does 'contentType:False' cause undefined index in PHP?

I have been trying to submit a form with enctype="multipart/form-data". I have this setting because the form will involve jpeg/png uploads once I have figured out the ajax submission for text inputs.

  1. the php works fine when referencing the script using action within the form html.

  2. the form data seems to be retrieved correctly by the below jquery because the alert line shows: productName=Test+Name&productDescription=Test+Description&OtherProductDetails=

  3. the returned data printed to my HTML by the jquery success function is a php error saying:Undefined index: productName

  4. removing contentType:false fixes the problem.

When i google jquery/ajax multipart/form-data submission, the top hits at least mainly include 'contentType:false'. Please could someone explain the reason to me?
Sending multipart/formdata with jQuery.ajax

The jquery API documentation says:
contentType (default: 'application/x-www-form-urlencoded; charset=UTF-8')
Type: String
When sending data to the server, use this content type.

Why would we need to set it to false for a multipart/form-data submission?
When would the false setting be needed at all?


$("#addProductForm").submit(function (event) {
//grab all form data
var formData = $(this).serialize();

url: 'addProduct.php',
type: 'POST',
data: formData,
async: false,
cache: false,
contentType: false,
processData: false,
success: function (returndata) {
error: function () {
alert("error in ajax form submission");

return false;


contentType option to false is used for multipart/form-data forms that pass files.

When one sets the contentType option to false, it forces jQuery not to add a Content-Type header, otherwise, the boundary string will be missing from it. Also, when submitting files via multi-part/form one must leave the processData flag set to false, otherwise, jQuery will try to convert your FormData into a string, which will fail.

To try and fix your issue:

You are using jQuery's .serialize() method which creates a text string in standard URL-encoded notation.

You need to pass un-encoded data when using "contentType: false".

Try using "new FormData" instead of .serialize():

  var formData = new FormData($(this)[0]);

See for yourself the difference of how your formData is passed to your php page by using console.log().

  var formData = new FormData($(this)[0]);

  var formDataSerialized = $(this).serialize();