rem计算

(function (win, doc) {
      if (!win.addEventListener) return;
      var html = document.documentElement;
      function setFont() {
          var html = document.documentElement;
          var k = 720;
          html.style.fontSize = html.clientWidth / k * 100 + "px";
      }
      setFont();
      setTimeout(function () {
          setFont();
      }, 300);
      doc.addEventListener('DOMContentLoaded', setFont, false);
      win.addEventListener('resize', setFont, false);
      win.addEventListener('load', setFont, false);
})(window, document);