var dpr, rem, scale;

var fontEl = document.createElement('style');

var metaEl = document.querySelector('meta[name="viewport"]');

var docEl = document.documentElement;

dpr = window.devicePixelRatio || 1;

rem = Math.ceil(docEl.clientWidth * 2 / 10);

scale = 1 / dpr;

// 设置viewport，进行缩放，达到高清效果

metaEl.setAttribute('content', 'width=' + dpr * rem + ',initial-scale=1,maximum-scale=1, minimum-scale=1,user-scalable=no');

// 设置data-dpr属性，留作的css hack之用

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

// 动态写入样式

docEl.firstElementChild.appendChild(fontEl);

fontEl.innerHTML = 'html{font-size:' + rem + 'px;}';

// 给js调用的，某一dpr下rem和px之间的转换函数

window.rem2px = function(v) {

    v = parseFloat(v);

    return v * rem;

};

window.px2rem = function(v) {

    v = parseFloat(v);

    return v / rem;

};

window.dpr = dpr;

window.rem = rem;