vue的自定義指令及常用使用場景

除了核心功能默認的內置指令（v-model和v-show）,也可以允許註冊自定義指令
代碼的複用和抽象是主要形式是組件，然而，有的情況系啊，你仍然需要對普通DOM進行底層操作

鉤子函數、鉤子函數參數、動態指令參數

常用場景總計如下：

1. 輸入框自動聚焦

// 註冊一個全局自定義指令 `v-focus`
Vue.directive('focus', {
  // 當被綁定的元素插入到 DOM 中時
  inserted: function (el) {
    // 聚焦元素
    el.focus()
  }
})


使用： <input v-focus>

2. 下拉菜單

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

new Vue({
  el: '#app',
  data: {
    show: false
  },
  methods: {
    handleHide() {
      this.show = false
    }
  }
})

使用如下：

<div class="main" v-menu="handleHide">
  <button @click="show = !show">點擊顯示下拉菜單</button>
  <div class="dropdown" v-show="show">
    <div class="item"><a href="#">選項 1</a></div>
    <div class="item"><a href="#">選項 2</a></div>
    <div class="item"><a href="#">選項 3</a></div>
  </div>
</div>

3.相對時間轉換
類似微博、朋友圈發佈動態後的相對時間，比如剛剛、兩分鐘前等等

new Vue({
  el: '#app',
  data: {
    time: 1565753400000
  }
})

Vue.directive('relativeTime', {
  bind(el, binding) {
    // Time.getFormatTime() 方法，自行補充
    el.innerHTML = Time.getFormatTime(binding.value)
    el.__timeout__ = setInterval(() => {
      el.innerHTML = Time.getFormatTime(binding.value)
    }, 6000)
  },
  unbind(el) {
    clearInterval(el.innerHTML)
    delete el.__timeout__
  }
})

4.滾動動畫

<div id="app">
  <h1 class="centered">Scroll me</h1>
  <div class="box" v-scroll="handleScroll">
    <p>Lorem ipsum dolor sit amet, consectetur adipisicing elit. A atque amet harum aut ab veritatis earum porro praesentium ut corporis. Quasi provident dolorem officia iure fugiat, eius mollitia sequi quisquam.</p>
  </div>
</div>

Vue.directive('scroll', {
  inserted: function(el, binding) {
    let f = function(evt) {
      if (binding.value(evt, el)) {
        window.removeEventListener('scroll', f)
      }
    }
    window.addEventListener('scroll', f)
  }
})

// main app
new Vue({
  el: '#app',
  methods: {
   handleScroll: function(evt, el) {
    if (window.scrollY > 50) {
      TweenMax.to(el, 1.5, {
        y: -10,
        opacity: 1,
        ease: Sine.easeOut
      })
    }
    return window.scrollY > 100
    }
  }
})

body {
  font-family: 'Abhaya Libre', Times, serif;
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
  background: #000;
  color: #fff;
  overflow-x: hidden;
}

h1,
h2,
h3,
h4 {
  font-family: 'Fira Sans', Helvetica, Arial, sans-serif;
  font-weight: 800;
}

.centered {
  margin: 0 auto;
  display: table;
  font-size: 60px;
  margin-top: 100px;
}

.box {
  border: 1px solid rgba(255, 255, 255, 0.5);
  padding: 8px 20px;
  line-height: 1.3em;
  opacity: 0;
  color: white;
  width: 200px;
  margin: 0 auto;
  margin-top: 30px;
  transform: translateZ(0);
  perspective: 1000px;
  backface-visibility: hidden;
  background: rgba(255, 255, 255, 0.1);
}

#app {
  height: 2000px;
}

5.頁面頂部標題

Vue.directive('title', {
    inserted: function (el, binding) {
        document.title = binding.value;
        el.remove();
    }
})