[html] JQuery: 'Uncaught TypeError: Illegal invocation' at ajax request - several elements

I have two select elements, A and B: when A's selected option changes, B's options must be updated accordingly. Each element in A implies many elements in B, it's a one-to-many relationship (A contains nations, B should contain cities located in the given nation).

The function do_ajax should run the asynchronous request:

function do_ajax(elem, mydata, filename)
{
    $.ajax({
        url: filename,
        context: elem,
        data: mydata,
        datatype: "html",
        success: function (data, textStatus, xhr) {
            elem.innerHTML = data;
        }
    });
}

In order to update B's options I've added a function call in A's onChange event. Here is the function that runs when onChange event (of A) is triggered:

function my_onchange(e) // "e" is element "A"
{
    var sel_B = ... ; // get select element "B"

    // I skipped some code here
    // ...

    var data = {
        'mode': 'filter_city',
        'id_A': e[e.selectedIndex]
    };
    do_ajax(city_sel, data, 'ajax_handler.php');
}

}

I've read in JQuery docs that data can be an array (key value pairs). I get the error if I put:

var data = {
        'mode': 'filter_city',
        'id_A': e[e.selectedIndex]
};

Instead, I don't get that error if my data is a string:

var data = 'mode=filter_city&id_A=' + e[e.selectedIndex];

But I need the "array version" of the variable, in my server-side php code.

The Uncaught TypeError: Illegal invocation is located in the "jquery-1.7.2.min.js" file, which is all compressed, so I couldn't figure out what part of code raised the error.

Is there any setting I can change in my code so that it accepts data as an associative array?

I've read in JQuery docs that data can be an array (key value pairs). I get the error if I put:

This is object not an array:

var data = {
        'mode': 'filter_city',
        'id_A': e[e.selectedIndex]
};

You probably want:

var data = [{
        'mode': 'filter_city',
        'id_A': e[e.selectedIndex]
}];

$.ajax({
                    url:"",
                    type: "POST",
                    data: new FormData($('#uploadDatabaseForm')[0]),
                    contentType:false,
                    cache: false,
                    processData:false,
                    success:function (msg) {}
                  });

Had the same issue recently, solved by adding traditional: true,

Please follow the procedure to get rid of this problem:

$.ajax({
   url: 'https://your-api-endpoint',
   type: 'post',
   data: new formData(this),
   processData: false,
   contentType: false,
   success: function(response) {
      console.log(response)
   }
})

You have to use processData: false and contentType: false, these two lines. Your problem will be solved.

From the jQuery docs for processData:

processData Boolean
^{Default: true}
By default, data passed in to the data option as an object (technically, anything other than a string) will be processed and transformed into a query string, fitting to the default content-type "application/x-www-form-urlencoded". If you want to send a DOMDocument, or other non-processed data, set this option to false.

Source: http://api.jquery.com/jquery.ajax

Looks like you are going to have to use processData to send your data to the server, or modify your php script to support querystring encoded parameters.

Try This:

            $.ajax({
                    url:"",
                    type: "POST",
                    data: new FormData($('#uploadDatabaseForm')[0]),
                    contentType:false,
                    cache: false,
                    processData:false,
                    success:function (msg) {}
                  });

I was getting this error while posting a FormData object because I was not setting up the ajax call correctly. Setup below fixed my issue.

var myformData = new FormData();        
myformData.append('leadid', $("#leadid").val());
myformData.append('date', $(this).val());
myformData.append('time', $(e.target).prev().val());

$.ajax({
    method: 'post',
    processData: false,
    contentType: false,
    cache: false,
    data: myformData,
    enctype: 'multipart/form-data',
    url: 'include/ajax.php',
    success: function (response) {
        $("#subform").html(response).delay(4000).hide(1); 
    }
});

function do_ajax(elem, mydata, filename)
{
    $.ajax({
        url: filename,
        context: elem,
        data: mydata,
        **contentType: false,
        processData: false**
        datatype: "html",
        success: function (data, textStatus, xhr) {
            elem.innerHTML = data;
        }
    });
}