移动端rem封装

(function(win, lib) {
     var doc = win.document;
     var docEl = doc.documentElement;
     var metaEl = doc.querySelector('meta[name="viewport"]');
     var flexibleEl = doc.querySelector('meta[name="flexible"]');
     var dpr = 0;
     var scale = 0;
     var tid;
     var flexible = lib.flexible || (lib.flexible = {});

     if (metaEl) {
 //        console.warn('将根据已有的meta标签来设置缩放比例');
         var match = metaEl.getAttribute('content').match(/initial\-scale=([\d\.]+)/);
         if (match) {
             scale = parseFloat(match[1]);
             dpr = parseInt(1 / scale);
         }
     } else if (flexibleEl) {
         var content = flexibleEl.getAttribute('content');
         if (content) {
             var initialDpr = content.match(/initial\-dpr=([\d\.]+)/);
             var maximumDpr = content.match(/maximum\-dpr=([\d\.]+)/);
             if (initialDpr) {
                 dpr = parseFloat(initialDpr[1]);
                 scale = parseFloat((1 / dpr).toFixed(2));
             }
             if (maximumDpr) {
                 dpr = parseFloat(maximumDpr[1]);
                 scale = parseFloat((1 / dpr).toFixed(2));
             }
         }
     }

     if (!dpr && !scale) {
         var isAndroid = win.navigator.appVersion.match(/android/gi);
         var isIPhone = win.navigator.appVersion.match(/iphone/gi);
         var devicePixelRatio = win.devicePixelRatio;
         if (isIPhone) {
             // iOS下，对于2和3的屏，用2倍的方案，其余的用1倍方案
             if (devicePixelRatio >= 3 && (!dpr || dpr >= 3)) {
                 dpr = 3;
             } else if (devicePixelRatio >= 2 && (!dpr || dpr >= 2)){
                 dpr = 2;
             } else {
                 dpr = 1;
             }
         } else {
             // 其他设备下，仍旧使用1倍的方案
             dpr = 1;
         }
         scale = 1 / dpr;
     }

     docEl.setAttribute('data-dpr', dpr);
     if (!metaEl) {
         metaEl = doc.createElement('meta');
         metaEl.setAttribute('name', 'viewport');
         metaEl.setAttribute('content', 'initial-scale=' + scale + ', maximum-scale=' + scale + ', minimum-scale=' + scale + ', user-scalable=no');
         if (docEl.firstElementChild) {
             docEl.firstElementChild.appendChild(metaEl);
         } else {
             var wrap = doc.createElement('div');
             wrap.appendChild(metaEl);
             doc.write(wrap.innerHTML);
         }
     }

     function refreshRem(){
         var width = docEl.getBoundingClientRect().width;
         console.log(width)
         if (width / dpr > 768) {
             width = 768 * dpr;
         }
         var rem = width / 6.4;
         docEl.style.fontSize = rem + 'px';
         flexible.rem = win.rem = rem;
     }

     win.addEventListener('resize', function() {
         clearTimeout(tid);
         tid = setTimeout(refreshRem, 300);
     }, false);
     win.addEventListener('pageshow', function(e) {
         if (e.persisted) {
             clearTimeout(tid);
             tid = setTimeout(refreshRem, 300);
         }
     }, false);

     if (doc.readyState === 'complete') {
         doc.body.style.fontSize = 12 * dpr + 'px';
     } else {
         doc.addEventListener('DOMContentLoaded', function(e) {
             doc.body.style.fontSize = 12 * dpr + 'px';
         }, false);
     }


     refreshRem();

     flexible.dpr = win.dpr = dpr;
     flexible.refreshRem = refreshRem;
     flexible.rem2px = function(d) {
         var val = parseFloat(d) * this.rem;
         if (typeof d === 'string' && d.match(/rem$/)) {
             val += 'px';
         }
         return val;
     }
     flexible.px2rem = function(d) {
         var val = parseFloat(d) / this.rem;
         if (typeof d === 'string' && d.match(/px$/)) {
             val += 'rem';
         }
         return val;
     }

 })(window, window['lib'] || (window['lib'] = {}));