flexible 精简版

看了 flexible 源码，不懂为什么对于android 没有缩放，而是粗放设置，导致 android 很不精细，于是略微删减代码如下，留着自己备用，后续如果再学到了什么知识点，再回顾吧。

本质上就是把 viewport 设置成物理像素大小，再缩小到屏幕独立像素这么大

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

    if (metaEl) {
      var match = metaEl.getAttribute('content').match(/initial\-scale=([\d\.]+)/);
      if (match) {
        scale = parseFloat(match[1]);
        dpr = parseInt(1 / scale);
      }
    }

    if (!dpr && !scale) {
      dpr = win.devicePixelRatio || 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;
      // 限制 rem 最大为 54px * dpr
      if (width / dpr > 540) {
        width = 540 * dpr;
      }
      var rem = width / 10;
      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'] = {}));