具体实现

/**
 * Created by taozh on 2017/5/6.
 * taozh2982@gmail.com
 */
var EleResize = {
 _handleResize: function (e) {
  var ele = e.target || e.srcElement;
  var trigger = ele.__resizeTrigger__;
  if (trigger) {
   var handlers = trigger.__z_resizeListeners;
   if (handlers) {
    var size = handlers.length;
    for (var i = 0; i < size; i++) {
     var h = handlers[i];
     var handler = h.handler;
     var context = h.context;
     handler.apply(context, [e]);
    }
   }
  }
 },
 _removeHandler: function (ele, handler, context) {
  var handlers = ele.__z_resizeListeners;
  if (handlers) {
   var size = handlers.length;
   for (var i = 0; i < size; i++) {
    var h = handlers[i];
    if (h.handler === handler && h.context === context) {
     handlers.splice(i, 1);
     return;
    }
   }
  }
 },
 _createResizeTrigger: function (ele) {
  var obj = document.createElement('object');
  obj.setAttribute('style',
   'display: block; position: absolute; top: 0; left: 0; height: 100%; width: 100%; overflow: hidden;opacity: 0; pointer-events: none; z-index: -1;');
  obj.onload = EleResize._handleObjectLoad;
  obj.type = 'text/html';
  ele.appendChild(obj);
  obj.data = 'about:blank';
  return obj;
 },
 _handleObjectLoad: function (evt) {
  this.contentDocument.defaultView.__resizeTrigger__ = this.__resizeElement__;
  this.contentDocument.defaultView.addEventListener('resize', EleResize._handleResize);
 }
};
if (document.attachEvent) {//ie9-10
 EleResize.on = function (ele, handler, context) {
  var handlers = ele.__z_resizeListeners;
  if (!handlers) {
   handlers = [];
   ele.__z_resizeListeners = handlers;
   ele.__resizeTrigger__ = ele;
   ele.attachEvent('onresize', EleResize._handleResize);
  }
  handlers.push({
   handler: handler,
   context: context
  });
 };
 EleResize.off = function (ele, handler, context) {
  var handlers = ele.__z_resizeListeners;
  if (handlers) {
   EleResize._removeHandler(ele, handler, context);
   if (handlers.length === 0) {
    ele.detachEvent('onresize', EleResize._handleResize);
    delete ele.__z_resizeListeners;
   }
  }
 }
} else {
 EleResize.on = function (ele, handler, context) {
  var handlers = ele.__z_resizeListeners;
  if (!handlers) {
   handlers = [];
   ele.__z_resizeListeners = handlers;

   if (getComputedStyle(ele, null).position === 'static') {
    ele.style.position = 'relative';
   }
   var obj = EleResize._createResizeTrigger(ele);
   ele.__resizeTrigger__ = obj;
   obj.__resizeElement__ = ele;
  }
  handlers.push({
   handler: handler,
   context: context
  });
 };
 EleResize.off = function (ele, handler, context) {
  var handlers = ele.__z_resizeListeners;
  if (handlers) {
   EleResize._removeHandler(ele, handler, context);
   if (handlers.length === 0) {
    var trigger = ele.__resizeTrigger__;
    if (trigger) {
     trigger.contentDocument.defaultView.removeEventListener('resize', EleResize._handleResize);
     ele.removeChild(trigger);
     delete ele.__resizeTrigger__;
    }
    delete ele.__z_resizeListeners;
   }
  }
 }
}

测试代码：

 
 
 
 


addListener
removeListener
resize

原理

这里的具体实现分两类，

• ie9-10
   

　　　　默认支持div的resize事件，可以直接通过div.attachEvent('onresize', handler);的方式实现

• 其它浏览器
   

　　　　通过在div中添加一个内置object元素实现监听。

　　　　设置object元素的style使其填充满div，这样当div的size发生变化时，object的size也会发生变化。

　　　　然后监听object元素的contentDocument.defaultView(window对象)的resize事件。