1. 上一次的问题总结。

• overflow:hidden -> body.appendChild
• 关闭重复 -> 分开,document 只管外面,popover 只管里面
• 忘了取消监听 document -> 收拢 close

2. 可以把一个函数哟没有五行作为一个优化的标准,简称为五行定律

3. 接下来把样式改好点

  .content-wrapper { // 如果写了scoped,popover里面那么就只作用于popover里面,移到外面就在外面了就可以
    position: absolute;
    border: 1px solid  $border-color;
    border-radius: $border-radius;
    filter: drop-shadow(0 0 1px rgba(0,0,0,0.5));
    /*通过drop-shadow解决小三角没有阴影的问题，但是兼容性不好 */
    /*box-shadow: 0 0 3px rgba(0, 0, 0, 0.5);*/
    background: white;
    transform: translateY(-100%);
    margin-top: -10px;
    padding: .5em 1em;
    max-width: 20em;
    word-break: break-all;
    &::before ,  &::after{
      content: '';
      display: block;
      width: 0;
      height: 0;
      position: absolute;
      border: 10px solid transparent;
      left: 10px;
    }
    &::after{
      content: '';
      display: block;
      width: 0;
      height: 0;
      position: absolute;
      border: 10px solid transparent;
      left: 10px;
    }
    &::before {
      border-top-color: black;
      top: 100%;
    }
    &::after {
      border-top-color: white;
      top: calc(100% - 1px);
    }
  }

4. 增加功能:用户可以选择 popover 是上面下面左面右面

  // 先要给contentWrapper加一个类,传递进入位置信息
  <div ref="contentWrapper" class="content-wrapper" v-if="visible"
    :class="{[`position-${position}`]:true}">
  </div>

  // 获得位置信息
  props: {
      position:{
        type: String,
        default: 'top',
        validator(value){
          return ['top','bottom','left','right'].indexOf(value) >= 0
        }
      }
    },
  }

  // 在method里面写方法,主要控制大概位置
  method: {
    positionContent() {
        const {contentWrapper, triggerWrapper} = this['$refs']
        document.body.appendChild(contentWrapper)
        let {width, height, top, left} = triggerWrapper.getBoundingClientRect()
        if(this.position === 'top'){
          contentWrapper.style.left = left + window.scrollX + "px"
          contentWrapper.style.top = top + window.scrollY + "px"
        }else if(this.position === 'bottom'){
          contentWrapper.style.left = left + window.scrollX + "px"
          contentWrapper.style.top = top + height + window.scrollY + "px"
        }else if(this.position === 'left'){
          contentWrapper.style.left = left + window.scrollX + "px"
          let {height: height2} = contentWrapper.getBoundingClientRect()
          contentWrapper.style.top = top  + window.scrollY + (height - height2)/2 + "px"
        }else if(this.position === 'right'){
          contentWrapper.style.left = left + window.scrollX + width + "px"
          let {height: height2} = contentWrapper.getBoundingClientRect()
          contentWrapper.style.top = top  + window.scrollY + (height - height2)/2 + "px"
        }
      },
  }

  // 然后对css进行处理,主要是箭头当想
  <style lang="scss" scoped>
  $border-color: #333;
  $border-radius: 4px;
  .popover {
    display: inline-block;
    vertical-align: top;
    position: relative;
  }
  .content-wrapper { // 如果写了scoped,popover里面那么就只作用于popover里面,移到外面就在外面了就可以
    position: absolute;
    border: 1px solid  $border-color;
    border-radius: $border-radius;
    filter: drop-shadow(0 0 1px rgba(0,0,0,0.5));
    /*通过drop-shadow解决小三角没有阴影的问题，但是兼容性不好 */
    /*box-shadow: 0 0 3px rgba(0, 0, 0, 0.5);*/
    background: white;
    padding: .5em 1em;
    max-width: 20em;
    word-break: break-all;
    &::before ,  &::after{
      content: '';
      display: block;
      border: 10px solid transparent;
      width: 0;
      height: 0;
      position: absolute;
    }

    &.position-top {
      transform: translateY(-100%);
      margin-top: -10px;
      &::before, &::after{
        left: 10px;
      }
      &::before {
        border-top-color: black;
        top: 100%;
      }
      &::after {
        border-top-color: white;
        top: calc(100% - 1px);
      }
    }

    &.position-bottom {
      margin-top: 10px;
      &::before, &::after{
        left: 10px;
      }
      &::before {
        border-bottom-color: black;
        bottom: 100%;
      }
      &::after {
        border-bottom-color: white;
        bottom: calc(100% - 1px);
      }
    }

    &.position-left{
      transform: translateX(-100%);
      margin-left: -10px;
      &::before, &::after{
        transform: translateY(-50%);
        top: 50%;
      }
      &::before {
        border-left-color: black;
        left: 100%;
      }
      &::after {
        border-left-color: white;
        left: calc(100% - 1px)
      }
    }

    &.position-right{
      margin-left: 10px;
      &::before, &::after{
        transform: translateY(-50%);
        top: 50%;
      }
      &::before {
        border-right-color: black;
        right: 100%;
      }
      &::after {
        border-right-color: white;
        right: calc(100% - 1px)
      }
    }

  }
</style>

5.发现目前代码比较冗余，进一步优化代码

• 多个 if else 逻辑相似，首先要把共有代码抽上去，利用表驱动编程的技巧。
  

  positionContent() {
        const {contentWrapper, triggerWrapper} = this['$refs']
        document.body.appendChild(contentWrapper)
        const {width, height, top, left} = triggerWrapper.getBoundingClientRect()
        const {height: height2} = contentWrapper.getBoundingClientRect()
        let positions = {
          top: {
            top: top + window.scrollY,
            left: left + window.scrollX
          },
          bottom: {
            top: top + height + window.scrollY,
            left: left + window.scrollX
          },
          left: {
            top: top  + window.scrollY + (height - height2)/2,
            left: left + window.scrollX
          },
          right: {
            top:  top  + window.scrollY + (height - height2)/2,
            left: left + window.scrollX + width
          },
        }
        contentWrapper.style.left = positions[this.position].left + 'px'
        contentWrapper.style.top = positions[this.position].top + 'px'
      },
  

6.实现 hover 的效果

// 每个事件的处理逻辑不一样，所以要分开写if
  mounted(){
    if(this.trigger === 'click'){
      this['$refs']['popover'].addEventListener('click',this.onClick)
    } else {
      this['$refs']['popover'].addEventListener('mouseenter',this.open)
      this['$refs']['popover'].addEventListener('mouseleave',this.close)
    }
  },
  // 负责任的轮子要写destory,防止内存泄露
  destroyed(){
    if(this.trigger === 'click'){
      this['$refs']['popover'].removeEventListener('click',this.onClick)
    } else {
      this['$refs']['popover'].removeEventListener('mouseenter',this.open)
      this['$refs']['popover'].removeEventListener('mouseleave',this.close)
    }
  },