/**
* 跨平臺(tái)的事件監(jiān)聽函數(shù)
* @param {Node} node 需要監(jiān)聽事件的DOM節(jié)點(diǎn)
* @param {String} eventType 需要監(jiān)聽的事件類型
* @param {Function} callback 事件監(jiān)聽回調(diào)函數(shù)
* @type Function 返回值為函數(shù)類型
* @return 返回監(jiān)聽回調(diào)函數(shù)的引用，用于釋放監(jiān)聽
*/
function bindEvent(node, eventType, callback) {
 if (node.attachEvent) {
  if (eventType.indexOf('on')) { eventType = 'on' + eventType;}
  node.attachEvent(eventType, callback);
 } else {
  if (!eventType.indexOf('on'))
   eventType = eventType.substring(2, eventType.length);
  node.addEventListener(eventType, callback, false);
 }
 return callback;
}
/**
* 跨平臺(tái)的事件監(jiān)聽卸載函數(shù)
* @param {Node} node 需要卸載監(jiān)聽事件的DOM節(jié)點(diǎn)
* @param {String} eventType 需要卸載監(jiān)聽的事件類型
* @param {Function} callback 卸載事件監(jiān)聽回調(diào)函數(shù)
*/
function removeEvent(node, eventType, callback) {
 if (node.detachEvent) {
  if (eventType.indexOf('on')) { eventType = 'on' + eventType;}
  node.detachEvent(eventType, callback);
 } else {
  if (!eventType.indexOf('on'))
   eventType = eventType.substring(2, eventType.length);
  node.removeEventListener(eventType, callback, false);
 }
}
/**
* 兼容不同定位方式的通用拖動(dòng)接口
* @param {Node} dragger 需要被拖動(dòng)的元素
*/
//必須告訴系統(tǒng)，哪些元素是可以進(jìn)行交互，而哪些是不行
function canDrag(dragger) {
 var drag = bindEvent(dragger,'onmousedown',function(e){
  //兼容事件對(duì)象
  e = e || event;
  //兼容坐標(biāo)屬性
  var pageX = e.clientX || e.pageX;
  var pageY = e.clientY || e.pageY;
  //兼容樣式對(duì)象
  var style = dragger.currentStyle || window.getComputedStyle(dragger,null);
  //當(dāng)沒有設(shè)置left和top屬性時(shí)，IE下默認(rèn)值為auto
  var offX = parseInt(style.left) || 0;
  var offY = parseInt(style.top) || 0;
  //獲取鼠標(biāo)相對(duì)于元素的間距
  var offXL = pageX - offX;
  var offYL = pageY - offY;
  //為dragger增加onDrag屬性，用來(lái)存儲(chǔ)拖動(dòng)事件
  if (!dragger.onDrag) {
   //監(jiān)聽拖動(dòng)事件
   dragger.onDrag = bindEvent(document,'onmousemove',function(e){
    e = e || event;
    var x = e.clientX || e.pageX;
    var y = e.clientY || e.pageY
    //設(shè)置X坐標(biāo)
    dragger.style.left = x - offXL + 'px';
    //設(shè)置Y坐標(biāo)
    dragger.style.top = y - offYL + 'px';
   });
   //監(jiān)聽拖動(dòng)結(jié)束事件
   dragger.onDragEnd = bindEvent(document,'onmouseup',function(e){
    //釋放前讀取事件對(duì)象
    var x = e.clientX || e.pageX;
    var y = e.clientY || e.pageY
    //釋放拖動(dòng)監(jiān)聽和結(jié)束監(jiān)聽
    removeEvent(document, 'onmousemove', dragger.onDrag);
    removeEvent(document, 'onmouseup', dragger.onDragEnd);
    try {
     //刪除拖動(dòng)時(shí)所用的屬性，兼容FF使用
     delete dragger.onDrag;
     delete dragger.onDragEnd;
    } catch (e) {
     //刪除拖動(dòng)時(shí)所用的屬性，兼容IE6使用
     dragger.removeAttribute('onDrag');
     dragger.removeAttribute('onDragEnd');
    }
   });
  }
 });
 return function() {
  //返回一個(gè)可以取消拖動(dòng)功能的函數(shù)引用
  //釋放拖動(dòng)監(jiān)聽和結(jié)束監(jiān)聽
  removeEvent(document, 'onmousemove', dragger.onDrag);
  removeEvent(document, 'onmouseup', dragger.onDragEnd);
  try {
   //刪除拖動(dòng)時(shí)所用的屬性，兼容FF使用
   delete dragger.onDrag;
   delete dragger.onDragEnd;
  } catch (e) {
   //刪除拖動(dòng)時(shí)所用的屬性，兼容IE6使用
   dragger.removeAttribute('onDrag');
   dragger.removeAttribute('onDragEnd');
  }
 }
}