Detailed explanation of Tooltip instance of Vue component

<template>
 <p style="position:relative;">
  <span ref="trigger">
   <slot>
   </slot>
  </span>
  <p class="tooltip"
   v-bind:class="{
    &#39;top&#39;:   placement === &#39;top&#39;,
    &#39;left&#39;:  placement === &#39;left&#39;,
    &#39;right&#39;:  placement === &#39;right&#39;,
    &#39;bottom&#39;: placement === &#39;bottom&#39;,
    &#39;disable&#39;: type === &#39;disable&#39;,
    &#39;delete&#39;: type === &#39;delete&#39;,
    &#39;visible&#39;: show === true 
   }"
   ref="popover"
   role="tooltip">
   <p class="tooltip-arrow"></p>
   <p class="tooltip-inner">
    <slot name="content" v-html="content"></slot>
   </p>
  </p>
 </p>
</template>

import EventListener from '../utils/EventListener.js';

export default {
 props: {
  // 需要监听的事件
  trigger: {
   type: String,
   default: 'click'
  },
  effect: {
   type: String,
   default: 'fadein'
  },
  title: {
   type: String
  },
  // toolTip消息提示
  content: {
   type: String
  },
  header: {
   type: Boolean,
   default: true
  },
  placement: {
   type: String
  }
 },
 data() {
  return {
   // 通过计算所得 气泡位置 
   position: {
    top: 0,
    left: 0
   },
   show: true
  };
 },
 watch: {
  show: function(val) {
   if (val) {
    const popover = this.$refs.popover;
    const triger = this.$refs.trigger.children[0];
    // 通过placement计算出位子
    switch (this.placement) {
     case 'top' :
      this.position.left = triger.offsetLeft - popover.offsetWidth / 2 + triger.offsetWidth / 2;
      this.position.top = triger.offsetTop - popover.offsetHeight;
      break;
     case 'left':
      this.position.left = triger.offsetLeft - popover.offsetWidth;
      this.position.top = triger.offsetTop + triger.offsetHeight / 2 - popover.offsetHeight / 2;
      break;
     case 'right':
      this.position.left = triger.offsetLeft + triger.offsetWidth;
      this.position.top = triger.offsetTop + triger.offsetHeight / 2 - popover.offsetHeight / 2;
      break;
     case 'bottom':
      this.position.left = triger.offsetLeft - popover.offsetWidth / 2 + triger.offsetWidth / 2;
      this.position.top = triger.offsetTop + triger.offsetHeight;
      break;
     default:
      console.log('Wrong placement prop');
    }
    popover.style.top = this.position.top + 'px';
    popover.style.left = this.position.left + 'px';
   }
  }
 },
 methods: {
  toggle() {
   this.show = !this.show;
  }
 },
 mounted() {
  if (!this.$refs.popover) return console.error("Couldn't find popover ref in your component that uses popoverMixin.");
  // 获取监听对象
  const triger = this.$refs.trigger.children[0];
  // 根据trigger监听特定事件
  if (this.trigger === 'hover') {
   this._mouseenterEvent = EventListener.listen(triger, 'mouseenter', () => {
    this.show = true;
   });
   this._mouseleaveEvent = EventListener.listen(triger, 'mouseleave', () => {
    this.show = false;
   });
  } else if (this.trigger === 'focus') {
   this._focusEvent = EventListener.listen(triger, 'focus', () => {
    this.show = true;
   });
   this._blurEvent = EventListener.listen(triger, 'blur', () => {
    this.show = false;
   });
  } else {
   this._clickEvent = EventListener.listen(triger, 'click', this.toggle);
  }
  this.show = !this.show;
 },
 // 在组件销毁前移除监听，释放内存
 beforeDestroy() {
  if (this._blurEvent) {
   this._blurEvent.remove();
   this._focusEvent.remove();
  }
  if (this._mouseenterEvent) {
   this._mouseenterEvent.remove();
   this._mouseleaveEvent.remove();
  }
  if (this._clickEvent) this._clickEvent.remove();
 }
};

// EventListener.js
const EventListener = {
 /**
  * Listen to DOM events during the bubble phase.
  *
  * @param {DOMEventTarget} target DOM element to register listener on.
  * @param {string} eventType Event type, e.g. 'click' or 'mouseover'.
  * @param {function} callback Callback function.
  * @return {object} Object with a `remove` method.
  */
 listen(target, eventType, callback) {
  if (target.addEventListener) {
   target.addEventListener(eventType, callback, false);
   return {
    remove() {
     target.removeEventListener(eventType, callback, false);
    }
   };
  } else if (target.attachEvent) {
   target.attachEvent('on' + eventType, callback);
   return {
    remove() {
     target.detachEvent('on' + eventType, callback);
    }
   };
  }
 }
};

export default EventListener;

<d-tooltip content="我是tooltip">
 <d-button type="text">鼠标移动到我上面试试</d-button>
</d-tooltip>
<d-tooltip content="我是tooltip" trigger="click">
 <d-button type="text">点我试试</d-button>
</d-tooltip>

<d-tooltip>
 <d-button type="text">鼠标移动到我上面试试</d-button>
 <p slot="content" class="tooltip-content">我是内容分发的conent。</p>
</d-tooltip>