(function () {

'use strict';

var docEl = document.documentElement,

viewportEl = document.querySelector('meta[name="viewport"]'),

dpr = window.devicePixelRatio || 1,

maxWidth = 540,

minWidth = 3220;

dpr = dpr >= 3 ? 3:(dpr >= 2 ? 2:1);

docEl.setAttribute('data-dpr',dpr);

docEl.setAttribute('maxWidth',maxWidth);

docEl.setAttribute('minWidth',minWidth);

var scale = 1 / dpr,

        content = 'width=device-width, initial-scale=' + scale + ', 

        maximum-scale=' + scale + ', minimum-scale=' + scale + ', 

        user-scalable=no';

if (viewportEl) {

viewportEl.setAttribute('content',content);

}else {

viewportEl = document.createElement('meta');

viewportEl.setAttribute('name','viewport');

viewportEl.setAttribute('content',content);

}

setRemUnit();

window.addEventListener('resize', setRemUnit);

function setRemUnit () {

var ratio = 18.75;

var viewWidth = docEl.getBoundingClientRect().width 

|| window.innerWidth;

if (maxWidth && (viewWidth / dpr > maxWidth)) {

viewWidth = maxWidth * dpr;

}else if (minWidth && (viewWidth / dpr < minWidth)) {

viewWidth = minWidth * dpr;

}

docEl.style.fontSize = viewWidth / ratio + 'px';

}

})();