再说移动端rem

将flexible.js 进行改进
参考 http://caibaojian.com/flexible-js.html 和 http://caibaojian.com/simple-flexible.html

1. flexible.js 源码中原文为 10 ,改为7.5 , 如设计稿为750, 就改为7.5; 此时rem 值为屏幕宽 / 7.5
2. 设计稿为640,,就改为6.4, 此时rem 值为屏幕宽 / 6.4
3. 必须给rem设置一个上限值, 当屏幕实际宽度大于750 ( 或640,即设计稿宽度 ) 时, rem 就为 100px,屏幕宽度即时增加,rem也不增大,
4. 在实际开发中, 100px100px 的元素就写成 1rem * 1rem, 30px30px的元素就写成 .3rem.3rem
5. 对于字体, 使用px作为单位
6. 以下是其源码 (10改为7.5 了)

;(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;
      if (width / dpr > 540) {
          width = 540 * dpr;
      }
      var rem = width / 7.5;
      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'] = {}));