效果

实现逻辑

• 监听鼠标按下事件，设置滑条背景色，left距离，记录初始位置，捕获鼠标
• 监听鼠标拖动事件，获取移动的距离，设置左侧区域与右侧区域的宽度，滑条的left值
• 监听鼠标松开事件，取消事件监听，恢复滑条背景色，释放鼠标

代码

<template>
  <div :class="prefixCls">
    <div ref="wrapRef" :class="`${prefixCls}-content`">
      <div ref="leftRef" :class="`${prefixCls}-aside`">
        <slot name="aside" />
      </div>

      <span ref="resizeRef" class="resize" />

      <div ref="rightRef" :class="[`${prefixCls}-main`, $slots.aside && 'ml']">
        <slot name="header" />
        <div :class="`${prefixCls}-main-content`">
          <slot />
        </div>
      </div>
    </div>
  </div>
</template>

<script>
export default {
  name: 'Demo',
  inheritAttrs: false
}
</script>

<script setup>
import { computed, onMounted, ref, unref, shallowRef } from 'vue'

const prefixCls = computed(() => 'page-layout')

const wrapRef = shallowRef()
const leftRef = ref()
const resizeRef = ref()
const rightRef = ref()

onMounted(() => dragController())

function dragController() {
  const leftEleMinWidth = 271
  const rightEleMinWidth = 500
  unref(resizeRef).onmousedown = function(e) {
    // 设置颜色
    resizeRef.value.style.background = '#3D8BF2'
    const startX = e.clientX
    resizeRef.value.left = unref(resizeRef).offsetLeft
    
    // 鼠标拖动
    document.onmousemove = function({ clientX }) {
      const endX = clientX
      // 移动距离
      let movingDistance = unref(resizeRef).left + (endX - startX)
      // 右边区域宽度
      const rightEleWidth = unref(wrapRef).clientWidth - unref(resizeRef).offsetWidth

	  // 拉伸的宽度不能小于左侧区域的宽度
      if (movingDistance < leftEleMinWidth) movingDistance = leftEleMinWidth
      // 判断最大宽度
      if (movingDistance > rightEleWidth - rightEleMinWidth) movingDistance = rightEleWidth - rightEleMinWidth

	 // 设置左侧区域宽度
      resizeRef.value.style.left = movingDistance
      leftRef.value.style.width = movingDistance + 'px'
      // 设置右侧区域宽度
      rightRef.value.style.width = (unref(wrapRef).clientWidth - movingDistance - 10) + 'px'
    }
    
    // 鼠标松开
    document.onmouseup = function() {
      resizeRef.value.style.background = '#fff'
      document.onmousemove = null
      document.onmouseup = null
      unref(resizeRef)?.releaseCapture?.()
    }
    unref(resizeRef)?.setCapture?.() // 设置鼠标捕获
    return false
  }
}
</script>

<style lang="scss">
.page-layout {
  overflow: hidden;
  display: flex;
  width: 100%;
  height: 100%;

  &-content {
    position: relative;
    overflow: hidden;
    flex: 1;
    display: flex;
    margin: 16px;
  }

  &-aside {
    overflow: hidden;
    width: 271px;
    padding: 16px 0 16px 16px;
  }

  &-main {
    flex: 1;
    display: flex;
    flex-direction: column;
    overflow: hidden;
    margin: 16px 16px 0;
    background-color: white;

    &-content {
      flex: auto;
      overflow: hidden;
      padding-top: 16px;
    }
  }

  .resize {
    width: 5px;
    margin: 16px 16px 11px 0;
    cursor: w-resize;
    background-color: #fff;
  }
  }
}
</style>