One way to do this is to simply use css and make sure that the element is a block level element, block level elements automatically occupy the entire width of the screen.
#fullscreen
{
height: 100vh;
background-image: url("http://placehold.it/500x500");
background-repeat: no-repeat;
background-size:cover;
}
Another solution is to use JavaScript by setting the width and height of the element to the width and height of the window.
var width = window.innerWidth;
var height = window.innerHeight;
var yourEl = document.getElementById('your elements Id');
yourEl.style.height = height + 'px';
yourEl.style.width = width + 'px';
, css
http://plnkr.co/edit/yatuyJj5941hCVNmoSwD?p=preview