vue项目左右布局（右侧布局是iframe） 中分线可拖拽及卡顿

功能需求：页面左右布局，左边初始定宽512px,右侧宽度 flex:1,分割线中间有拖拽按钮，拖拽时 左侧的宽度最大宽度是现在宽度+现在宽的的50%。最小宽度是初始宽度的一半 。

解决思路：在mounted生命周期，监听分割线DOM的onmousedown事件，在拖拽过程中动态计算，然后赋值改变左右DOM元素的宽度。

实现代码：（class类里用的tailwindcss）

<!--template-->
 <div class={['flex h-full']}>
     <div class={[style.subject__left_container, 'relative']} ref='leftDom'>
        左侧内容区
      </div>
   <div class='flex-1 flex h-full relative'>
       {this.envHost && <iframe src={this.envHost} style='height:100%; width:100%'/>}
       {!this.envHost && <Empty/>
   </div>
</div>

<!--css-->
.subject__left_container {
  width: 512px;
  border-right: 1px solid #e8e8e8;
}

<!--js-->
  // mounted生命周期
  public mounted() {
    this.leftDom = this.$refs.leftDom;
    let moveDom = this.$refs.moveDom;
    (moveDom as any).onmousedown = (e: any) => {
      this.clientStartX = e.clientX;
      e.preventDefault();
  
      document.onmousemove = (e) => {
        this.moveHandle(e.clientX, this.leftDom);
      };

      document.onmouseup = () => {
        document.onmouseup = null;
        document.onmousemove = null;
      };
    };
  }

 public moveHandle(nowClientX: number, letfDom: any) {
    let computedX = nowClientX - this.clientStartX;
    let leftBoxWidth = parseInt(letfDom.clientWidth);
    let changeWidth = leftBoxWidth + computedX;
    if (changeWidth < 256) {
      changeWidth = 256;
    }

    if (changeWidth > 768) {
      changeWidth = 768;
    }
    letfDom.style.width = changeWidth + 'px';
    this.clientStartX = nowClientX;
  }

🚩注意： 以上代码对左右布局都是div的话 是ok的，但是当我们右边的布局里有iframe，单纯这么写，拖拽时鼠标移入右侧iframe区时会拖不动，或者无法根据鼠标移动，快速响应，甚至在监听鼠标的按下和松开事件上都有明显的卡顿问题。

解决方法：在拖动的时候，在iframe上方添加一个透明的遮罩层，然后在停止拖拽的时候让其消失。

<!--template-->
 <div class={['flex h-full']}>
     <div class={[style.subject__left_container, 'relative']} ref='leftDom'>
        左侧内容区
      </div>
   <div class='flex-1 flex h-full relative'>
      <div class={style.iframe__div} ref='iframeDiv'/>
       {this.envHost && <iframe src={this.envHost} style='height:100%; width:100%'/>}
       {!this.envHost && <Empty/>
   </div>
</div>

<!--css-->
.subject__left_container {
  width: 512px;
  border-right: 1px solid #e8e8e8;
}

.iframe__div {
  width:100%;
  height: 100%;
  position: absolute;
  z-index: 999;
  filter: alpha(opacity=0);
  opacity: 0;
  background: transparent;
  display: none;
}

<!--js-->
  // mounted生命周期
  public mounted() {
    this.leftDom = this.$refs.leftDom;
    let moveDom = this.$refs.moveDom;
    var iframeDiv = this.$refs.iframeDiv;
    (moveDom as any).onmousedown = (e: any) => {
      this.clientStartX = e.clientX;
      e.preventDefault();
      if (iframeDiv) {
        (iframeDiv as any).style.display = 'block';
      }
      document.onmousemove = (e) => {
        this.moveHandle(e.clientX, this.leftDom);
      };

      document.onmouseup = () => {
       if (iframeDiv) {
          (iframeDiv as any).style.display = 'none';
        }
        document.onmouseup = null;
        document.onmousemove = null;
      };
    };
  }

 public moveHandle(nowClientX: number, letfDom: any) {
    let computedX = nowClientX - this.clientStartX;
    let leftBoxWidth = parseInt(letfDom.clientWidth);
    let changeWidth = leftBoxWidth + computedX;
    if (changeWidth < 256) {
      changeWidth = 256;
    }

    if (changeWidth > 768) {
      changeWidth = 768;
    }
    letfDom.style.width = changeWidth + 'px';
    this.clientStartX = nowClientX;
  }