XMLHttpRequest not adding header - "X-Requested-With: XMLHttpRequest"

Question

I have an ajax call where I used jQuery.ajax() to make a request to an mvc action. This all worked fine. However due to some forms having a file control I changed it from using jQuery.ajax() to using the XMLHttpRequest to send it using the HTML5 File API.

Since making this change the MVC action method no longer see's it as an ajax request. Using Fiddler2 I have noticed that it no longer adds the "X-Requested-With: XMLHttpRequest" to the request and I assume this is the problem.

The form I am trying to send does not have a file input in it, only normal textboxes etc, but I was trying to keep the method generic to deal with both. The following is the code I am using to send the ajax request:

// get the edit tender form
var $Form = $Button.closest('form');
var Url = $Form.attr('action');
var AjaxRequestObject = new XMLHttpRequest();
var FormDataToSend = new FormData();

$Form.find(':input').each(function () {
    if ($(this).is('input[type="file"]')) {
        var files = $(this)[0].files;
        if (files.length > 0) {
            FormDataToSend.append(this.name, files[0]);
        }
    } else {
        FormDataToSend.append(this.name, $(this).val());
    }
});

AjaxRequestObject.open('POST', Url, true);
AjaxRequestObject.onreadystatechange = function () {
    if (AjaxRequestObject.readyState == 4) {
        // handle response.
        if (AjaxRequestObject.status == 200) {
            if (!AjaxErrorExists(AjaxRequestObject.responseText, )) {
                alert("success");
                console.log(AjaxRequestObject.responseText);
            }
            else {
                alert('failure');
            }
        }
        else {
            alert('failure');
        }
    }
};

AjaxRequestObject.send(FormDataToSend);

This code was provided following a problem I had which Darin Dimitrov provided the solution to, so I could send the file inputs by ajax.

Any ideas why this request would not send the header for an ajax call?

Answer 1

X-Requested-With is automatically added by jQuery. You can just as easily add it yourself with AjaxRequestObject.setRequestHeader(). Docs

Answer 2

I was having troubles with detecting if my request was ajax. So, maybe this sample will save someone a minute or two:

var xmlhttp = new XMLHttpRequest();
xmlhttp.open('GET', URL, true);  // `true` for async call, `false` for sync.

// The header must be after `.open()`, but before `.send()`
xmlhttp.setRequestHeader('X-Requested-With', 'XMLHttpRequest');

xmlhttp.onreadystatechange = function() {
    // 4th state is the last:
    if (xmlhttp.readyState == 4 && xmlhttp.status == 200) { ... }
};
xmlhttp.send();

Tested with Flask.