<button onclick="launchFullscreen(document.documentElement);"></button>

        function launchFullscreen(element) {

            if (element.requestFullscreen) {

                element.requestFullscreen();

            } else if (element.mozRequestFullScreen) {

                element.mozRequestFullScreen();

            } else if (element.webkitRequestFullscreen) {

                element.webkitRequestFullscreen();

            } else if (element.msRequestFullscreen) {

                element.msRequestFullscreen();

            }

        }