// 阻止拖动看到“powered by...”
    // 查看el是否存在selector对应的父dom
    function closest(el, selector) {
      var matchesFn;
      // find vendor prefix
      ['matches','webkitMatchesSelector','mozMatchesSelector','msMatchesSelector','oMatchesSelector'].some(function(fn) {
          if (typeof document.body[fn] == 'function') {
              matchesFn = fn;
              return true;
          }
          return false;
      })

      var parent;

      // traverse parents
      while (el) {
          parent = el.parentElement;
          if (parent && parent[matchesFn](selector)) {
              return parent;
          }
          el = parent;
      }
      return null;
    }

    var _startX = 0,
    _startY = 0,
    _currentSelector;

    function _touchStart(e) {
      if (e.target.className === 'active-state' || closest(e.target, '#eruda')) {
          return;
      }
      if (!closest(e.target, _currentSelector)) {
        // console.log('非需要拖拽的区域')
        e.preventDefault()
        return;
      }
      try {
          var touch = e.touches[0],
              x = Number(touch.pageX),
              y = Number(touch.pageY);
          _startX = x;
          _startY = y;
      } catch (e) {
          alert(e);
      }
    }
    // document.addEventListener('touchstart', _touchStart);
    function initScrollDom(selector) {
      return;
      _currentSelector = selector
      var ele = document.querySelector(selector);
     
      
      // ele.ontouchmove 
      var _touchMove = function (e) {
          var point = e.touches[0],
              eleTop = ele.scrollTop,
              eleScrollHeight = ele.scrollHeight,
              eleOffsetHeight = ele.offsetHeight,
              eleTouchBottom = eleScrollHeight - eleOffsetHeight;
          // console.log('----------------------------')
          // console.log(eleTop)
          // console.log(eleTouchBottom)
          // console.log(point.clientY)
          // console.log(_startY)
          // console.log('----------------------------')
          if (eleTop === 0) {
              if (point.clientY > _startY) {
                  e.preventDefault();
              }
          } else if (eleTop === eleTouchBottom) {
              if (point.clientY < _startY) {
                  e.preventDefault()
              }
          }
      };
      ele.removeEventListener('touchmove', _touchMove);
      ele.addEventListener('touchmove', _touchMove);

    }