Ajax File Upload Issue

As per the demo link that you have provided Ajax File Upload , the upload file will be posted to upload.php

Now, where to write this upload.php name, Simple ,

<form id="upload" method="post" action="upload.php" enctype="multipart/form-data">
            <div id="drop">
                Drop Here

                <a>Browse</a>
                <input type="file" name="upl" multiple="">
            </div>

            <ul>
                <!-- The file uploads will be shown here -->
            </ul>

        </form>

In the above code, form action data action="upload.php" decide the post url name. SO let say if you want to post to some controller action method, then instead of upload.php write down your controller action method name.

For different url, please try

$(function(){

var ul = $('#attachments_plugin ul');

$('#drop a').click(function(){
    // Simulate a click on the file input button
    // to show the file browser dialog
    $(this).parent().find('input').click();
});

// Initialize the jQuery File Upload plugin
$('#attachments_plugin').fileupload({
    url: '/path/to/upload/',

    // This element will accept file drag/drop uploading
    dropZone: $('#drop'),

    // This function is called when a file is added to the queue;
    // either via the browse button, or via drag/drop:
    add: function (e, data) {

        var tpl = $('<li class="working"><input type="text" value="0" data-width="20" data-height="20"'+
            ' data-fgColor="#0788a5" data-readOnly="1" data-bgColor="#3e4043" /><p></p><span></span></li>');

        // Append the file name and file size
        tpl.find('p').text(data.files[0].name)
                     .append('<i>' + formatFileSize(data.files[0].size) + '</i>');

        // Add the HTML to the UL element
        data.context = tpl.appendTo(ul);

        // Initialize the knob plugin
        tpl.find('input').knob();

        // Listen for clicks on the cancel icon
        tpl.find('span').click(function(){

            if(tpl.hasClass('working')){
                jqXHR.abort();
            }

            tpl.fadeOut(function(){
                tpl.remove();
            });

        });

        // Automatically upload the file once it is added to the queue
        var jqXHR = data.submit();
    },

    progress: function(e, data){

        // Calculate the completion percentage of the upload
        var progress = parseInt(data.loaded / data.total * 100, 10);

        // Update the hidden input field and trigger a change
        // so that the jQuery knob plugin knows to update the dial
        data.context.find('input').val(progress).change();

        if(progress == 100){
            data.context.removeClass('working');
        }
    },

    fail:function(e, data){
        // Something has gone wrong!
        data.context.addClass('error');
    }

});


// Prevent the default action when a file is dropped on the window
$(document).on('drop dragover', function (e) {
    e.preventDefault();
});

// Helper function that formats the file sizes
function formatFileSize(bytes) {
    if (typeof bytes !== 'number') {
        return '';
    }

    if (bytes >= 1000000000) {
        return (bytes / 1000000000).toFixed(2) + ' GB';
    }

    if (bytes >= 1000000) {
        return (bytes / 1000000).toFixed(2) + ' MB';
    }

    return (bytes / 1000).toFixed(2) + ' KB';
}

});