『REM』手机屏幕适配

function adapt(designWidth, rem2px){

  var d = window.document.createElement(‘div‘);

  d.style.width = ‘1rem‘;

  d.style.display = "none";

  var head = window.document.getElementsByTagName(‘head‘)[0];

  head.appendChild(d);

  var defaultFontSize = parseFloat(window.getComputedStyle(d, null).getPropertyValue(‘width‘));

  d.remove();

  document.documentElement.style.fontSize = window.innerWidth / designWidth * rem2px / defaultFontSize * 100 + ‘%‘;

  var st = document.createElement(‘style‘);

  var portrait = "@media screen and (min-width: "+window.innerWidth+"px) {html{font-size:"+((window.innerWidth/(designWidth/rem2px)/defaultFontSize)*100) +"%;}}";

  var landscape = "@media screen and (min-width: "+window.innerHeight+"px) {html{font-size:"+((window.innerHeight/(designWidth/rem2px)/defaultFontSize)*100) +"%;}}"

  st.innerHTML = portrait + landscape;

  head.appendChild(st);

  return defaultFontSize

};

var defaultFontSize = adapt(640, 100);