JQuery POP UP during page load /Post back

give call to below fuction on client click

function ShowLoading(e) {
        var div = document.createElement('div');
        var img = document.createElement('img');
        img.src = '/_layouts/Portal/Images/ajax-loader-1.gif';
        div.innerHTML = "Please wait...<br />";
        div.style.cssText = 'position: fixed; top: 30%; left: 40%; z-index: 5000; width: 222px; text-align: center; background: #fff; border: 1px solid #000';
        div.appendChild(img);
        document.body.appendChild(div);
       
    }