添加事件

addEvent.js

function addListener(element, type, handler) {
  if (element.addEventListener) {
    element.addEventListener(type, handler, false);
    return handler;
  } else if (element.attachEvent) {
    var wrapper = function() {
      var event = window.event;
      event.target = event.srcElement;
      handler.call(element, event);
    }
    element.attachEvent('on' + type, wrapper)
    return wrapper;
  }
}