实现左侧导航菜单可拖拽改变导航宽度
实现效果：

html大致结构是这样的

 <el-scrollbar
      id="leftmenu"
      v-resize="MuneResize"
      wrap-class="scrollbar-wrapper"
    >
      <el-menu
        :default-active="activeMenu"
        :collapse="isCollapse"
        :background-color="variables.menuBg"
        :text-color="variables.menuText"
        :unique-opened="false"
        :active-text-color="variables.menuActiveText"
        :collapse-transition="false"
        mode="vertical"
      >
        <sidebar-item
          v-for="route in routes"
          :key="route.path"
          :item="route"
          :base-path="route.path"
        />
      </el-menu>
    </el-scrollbar>
    <!-- 给个可以拖拽的标识 -->
    <div id="drap-meuline" />

 // 自定义指令 获取当前菜单的宽度
  directives: {
    resize: {
      // 指令的名称
      bind(el, binding) {
        // el为绑定的元素，binding为绑定给指令的对象
        let _width = "";
        function isReize() {
          const style = document.defaultView.getComputedStyle(el);
          if (_width !== style.width) {
            binding.value({ width: style.width, targetId: el.id });
            _width = style.width;
          }
        }
        el.__vueSetInterval__ = setInterval(isReize, 300);
      },
      unbind(el) {
        clearInterval(el.__vueSetInterval__);
      },
    },
  },
mounted() {
    // 获取dom，对左菜单进行拖拽
    var drapLine = document.getElementById("drap-meuline");
    // 获取右侧内容Dom
    var mainContainer = document.getElementsByClassName("main-container")[0];
    // 获取左侧菜单Dom
    var menuleft = document.getElementById("leftmenu");
    // 获取左侧菜单Dom父元素，为了动态设置宽度
    var sidebarWidth = document.getElementsByClassName("sidebar-container")[0];

    // 是否需要本地保存
    // const history_width = localStorage.getItem("sliderWidth");
    // if (history_width) {
    //   sidebarWidth.style.width = history_width;
    //   mainContainer.style.marginLeft = history_width;
    // }
    drapLine.onmousedown = function (e) {
      // 设置最大/最小宽度
      var max_width = 600;
      var min_width = 210;
      let mouse_x = 0; // 记录鼠标相对left盒子x轴位置
      e.preventDefault(); // 阻止默认事件
      const _e = e || window.event;
      mouse_x = _e.clientX - menuleft.offsetWidth;
      document.onmousemove = function (e_) {
        console.log(min_width, max_width);
        const _e_ = e_ || window.event;
        let left_width = _e_.clientX - mouse_x;
        left_width = left_width < min_width ? min_width : left_width;
        left_width = left_width > max_width ? max_width : left_width;
        sidebarWidth.style.width = left_width + "px";
        mainContainer.style.marginLeft = left_width + "px";
      };
      document.onmouseup = function (e) {
        document.onmousemove = null;
        document.onmouseup = null;
        // 本地保存
        // localStorage.setItem("sliderWidth", menuleft.style.width);
      };
    };
  },

//拖拽宽度的改变
methods：{
 // 动态获取左侧菜单的宽度
   MuneResize(data) {
     // 拿到左侧菜单父元素
     const leftDom = document.getElementById(`${data.targetId}`);
     // 拿到右侧内容父元素
     const mainContainer =
       document.getElementsByClassName("main-container")[0];
       mainContainer.style.marginLeft = leftDom.clientWidth + "px";
    },
}

大概样式：

#app .sidebar-container {
  display: flex;
}
#drap-meuline {
  background: transparent;
  width: 4px;
  cursor: e-resize; //设置鼠标悬浮上去显示可拖拽样式
}