upload multiple image files

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ASP.NET

jQuery

I am very new to jquery. I got a requirement where i need to upload multiple image files using jquery with progress bar. i googled it found the solution, but i could'nt understand the jquery script. So can any one explain me the logic.

Link :- Upload multiple file in asp.net using jquery

Code:-

$(document).ready(function () {
            $("#btnUpload").click(function (evt) {
                /* variables */
                var status = $('.status');
                var percent = $('.percent');
                var bar = $('.bar');
                $('form').ajaxForm({
                    url: "FileUploadHandler.ashx",
                    type: "POST",
                    /* reset before submitting */
                    beforeSend: function () {
                        status.fadeOut();
                        bar.width('0%');
                        percent.html('0%');
                    },
 
                    /* progress bar call back*/
                    uploadProgress: function (event, position, total, percentComplete) {
                        var pVel = percentComplete + '%';
                        bar.width(pVel);
                        percent.html(pVel);
                    },
 
                    /* complete call back */
                    complete: function (data) {
                        status.html(data.responseText).fadeIn().fadeOut(1600); 
 
                    }
 
                });
 
            });
        });