JS 外观模式

function addEvent(dom, type, fn) {
  if (dom.addEventListener) {      // 支持DOM2级事件处理方法的浏览器
    dom.addEventListener(type, fn, false)
  } else if (dom.attachEvent) {    // 不支持DOM2级但支持attachEvent
    dom.attachEvent('on' + type, fn)
  } else {
    dom['on' + type] = fn      // 都不支持的浏览器
  }
}

const myInput = document.getElementById('myinput')
addEvent(myInput, 'click', function() {console.log('绑定 click 事件')})

const getEvent = function(event) {  // 获取事件对象
  return event || window.event      // IE下window.event
}

const getTarget = function(event) {        // 获取事件元素
  const event = getEvent(event)
  return event.target || event.srcElement  // IE下event.srcElement
}

const preventDefault = function(event) {    // 阻止默认事件
  const event = getEvent(event)
  if (event.preventDefault) {event.preventDefault()}
  else {event.returnValue = false}          // IE下
}

const cancelBubble = function(event) {
  const event = getEvent(event)
  if (event.stopPropagation) {event.stopPropagation()}
  else {event.cancelBubble = true}      // IE下
}

document.onclick = function(e) {
  preventDefault(e)
  if (getTarget(e) !== document.getElementById('myinput')) {console.log('呵呵')}
}