~~~ (function (doc, win) { var docEl = doc.documentElement, resizeEvt = 'orientationchange' in window ? 'orientationchange' : 'resize', recalc = function () { var clientWidth = docEl.clientWidth; if (!clientWidth) return; if (clientWidth >= 1920) { docEl.style.fontSize = '100px'; } else { docEl.style.fontSize = 100 * (clientWidth / 1920) + 'px'; } }; if (!doc.addEventListener) return; win.addEventListener(resizeEvt, recalc, false); doc.addEventListener('DOMContentLoaded', recalc, false); })(document, window); ~~~