提问

写一个通用事件侦听器

一个通用事件侦听器 需要考虑到 浏览器的兼容问题， 在旧浏览器、IE浏览器、现代浏览器中，事件侦听的绑定和移除均有所差别，而且 event 也有差别。

const DomEvent = {
  add: function (el, type, handler) {
    if (el.addEventListener) {
      el.addEventListener(type, handle, false);
    } else if (el.attachEvent) {
      el.attachEvent('on' + type, handler);
    } else {
      el['on' + type] = handler;
    }
  },
  remove: function (el, type handler) {
    if (el.removeEventListener) {
      el.removeEventListener(type, handler, false);
    } else if (el.detachEvent) {
      el.detachEvent('on' + type, handler);
    } else if {
      el['on' + type] = null;
    }
  },
  getTarget: function (event) {
    return event.target || event.srcElement;
  },
  getEvent: function (event) {
    return event || window.event;
  },
  stopPropagation: function (event) {
    if (event.stopPropagation) {
      event.stopPropagation();
    } else {
      event.cancelBubble = true;
    }
  },
  preventDefault: function (event) {
    if (event.preventDefault) {
      event.preventDefault();
    } else {
      event.returnValue = false;
    }
  }
}