详解Vue用自定义指令完成一个下拉菜单（select组件）

//全局注册
Vue.directive('my-directive', {
 // 指令选项
})

// 局部注册
var app = new Vue({
 el: '#app'
 directives: {
  'my-directive': {
    // 指令选项
  }
})

// html部分
<div id="app" v-focus>
// js部分
Vue.directive('focus', {
 // 当绑定元素插入到 DOM 中。
 inserted: function (el) {
  // 聚焦元素
  el.focus()
 }
})

// HTML部分
<div id="app" v-demo:msg.a.b="message">
 <div v-text:msg.a.b="message"></div>
</div>
// JS部分
Vue.directive('demo', {
 bind: function (el, binding, vnode) {
  var s = JSON.stringify
  el.innerHTML =
   'name: '    + binding.name + '<br>' +
   'value: '   + binding.value + '<br>' +
   'expression: ' + binding.expression + '<br>' +
   'argument: '  + binding.arg + '<br>' +
   'modifiers: ' + JSON.stringify(binding.modifiers).modifiers + '<br>' +
   'vnode keys: ' + Object.keys(vnode).join(',')
 }
})
new Vue({
 el: '#app',
 data: {
  message: 'some text'
 }
})

name: "test"
value: "some text"
expression: "message"
argument: "msg"
modifiers: {"a":true,"b":true}
vnode keys: tag, data, children, text, elm, ns, context, functionalContext, functionalOptions, functionalScopeId, key, componentOptions, componentInstance, parent, raw, isStatic, isRootInsert, isComment, isCloned, isOnce, asyncFactory, asyncMeta, isAsyncPlaceholder

// HTML部分
<div id="app" v-demo:msg.a.b="message">
 <div v-test="{msg: 'hello', name: 'Aresn'}"></div>
</div>

//JS部分
Vue.directive('test', {
 bind: function (el, binding, vnode) {
  console.log(binding.value.msg)
  console.log(binding.value.name)
 }
})
var app = new Vue({
 el: '#app'
})

// HTML部分
<div id="app" v-clock>
 <div class="main" v-clickoutside="handleClose">
  <button @click="show = !show">点击显示下拉菜单</button>
  <div class="dropdown" v-show="show">
   <p>下拉框内容，点击外面区域可以关闭</p>
  </div>
</div>

// JS部分
var app = new Vue({
 el: '#app',
 data: {
  show: false
 }，
methods: {
 handleClose() {
  this.show = false;
 }
}
})

Vue.directive('clickoutside', {
 bind: function(el, binding, vode) {
  function documentHandler (e) {
   if (el.contains(e.target)) {
    return false
   }
   if (binding.expression) {
    binding.value(e)
   }
  }
  el.__vueClickOutSide__ = documentHandler
  document.addEventListener('click', documentHandler)
 },
 unbind: function(el, binding) {
  document.removeEventListener('click', el.__vueClickOutSide__)
  delete el.__vueClickOutSide__
 }
})

// HTML
<div id="parent">
 父元素
 <div id="children">子元素</div>
</div>
// JS
var a = doucment.getElemengById('parent')
var b = doucment.getElemengById('children')
console.log(A.contains(B)) // true
console.log(B.contains(A)) // false