首先来总结element ui 官方文档的左侧菜单结构,带有el-submenu为子级节点,el-menu-item表示没有下级。当然,菜单不能写死，因为菜单也许不止两级,所以我们需要递归来实现。根据当前节点是否有下级去判断,如果有下级,则继续调用子级,直到没有下级为止,下面我贴上左侧菜单所有的代码:

• 请求数据格式

[
      {
        name: "首页",
        id: -1,
        icon: "el-icon-picture-outline-round",
        url: "/index",
        children: []
      },
      {
        name: "按钮",
        id: 20,
        icon: "el-icon-message-solid",
        url: "/button",
        children: []
      },
      {
        name: "测试1",
        id: 1,
        icon: "el-icon-s-claim",
        url: "",
        children: [
          {
            id: 4,
            parentid: 1,
            name: "测试1-1",
            icon: "el-icon-chat-dot-round",
            url: "",
            children: [
              {
                id: 8,
                parentid: 1,
                name: "测试1-1-1",
                icon: "el-icon-cloudy",
                url: "/test",
                children: []
              },
              {
                id: 9,
                parentid: 1,
                name: "测试1-1-2",
                icon: "el-icon-files",
                url: "/test1",
                children: []
              }
            ]
          },
          {
            id: 5,
            parentid: 1,
            name: "测试1-2",
            icon: "el-icon-shopping-cart-1",
            url: "/test3",
            children: []
          }
        ]
      },
      {
        name: "测试2",
        id: 2,
        icon: "el-icon-menu",
        url: "",
        children: [
          {
            id: 6,
            parentid: 2,
            name: "测试2-1",
            icon: "el-icon-folder-checked",
            url: "",
            children: []
          },
          {
            id: 7,
            parentid: 2,
            name: "测试2-2",
            icon: "el-icon-folder-remove",
            url: "",
            children: []
          }
        ]
      },
      {
        name: "测试3",
        id: 3,
        icon: "el-icon-monitor",
        url: "",
        children: []
      }
    ]

• menu.vue

<template>
  <div class="menu">
    <div class="logo-con">
      <div class="title" v-show="!collapse">
        <span class="title__sider-title is-active">{{logo}}</span>
      </div>
      <div class="title" v-show="collapse">
        <span class="title__sider-title el-tag--mini">LG</span>
      </div>
    </div>
    <el-menu
      :background-color="backgroundColor"
      :text-color="textColor"
      :default-active="$route.meta.pageId"
      :collapse="collapse"
    >
      <template v-for="item in list">
        <router-link :to="item.url" :key="item.id" v-if="item.children.length===0">
          <el-menu-item :index="item.id.toString()">
            <i :class="item.icon"></i>
            <span slot="title">{{item.name}}</span>
          </el-menu-item>
        </router-link>
        <subMenu v-else :data="item" :key="item.id"></subMenu>
      </template>
    </el-menu>
  </div>
</template>

<script>
import subMenu from "./subMenu";
export default {
  name: "menuList",
  components: {
    subMenu
  },
  data() {
    return {
      collapse: false, //是否折叠
      list: [], //当行菜单数据源
      backgroundColor: "#304156", //导航菜单背景颜色
      textColor: "#BFCBD9", //导航菜单文字颜色
      logo: "LOGO" //logo
    };
  }
};
</script>

<style lang="scss" scoped>
.el-menu {
  border-right: none;
  a {
    text-decoration: none;
  }
}
.logo-con {
  height: 64px;
  padding: 10px;

  .title {
    position: relative;
    text-align: center;
    font-size: 20px;
    height: 64px;
    line-height: 64px;

    span {
      padding: 0 5px 0 0;
      color: #409eff;
      font-size: 20px;
    }
  }
}
</style>

• submenu.vue
  这里有个知识点functional,不懂自行百度,文档地址:https://cn.vuejs.org/v2/guide/render-function.html#%E5%87%BD%E6%95%B0%E5%BC%8F%E7%BB%84%E4%BB%B6

<!--
 * @Description: 
 * @Author: PYH
 * @Date: 2019-08-07
 -->
<template functional>
  <el-submenu :index="props.data.id.toString()">
    <template slot="title">
      <i :class="props.data.icon"></i>
      <span>{{props.data.name}}</span>
    </template>
    <template v-for="item in props.data.children">
      <router-link :to="item.url" :key="item.id" v-if="item.children.length===0">
        <el-menu-item class="subitem" :index="item.id.toString()">
          <i :class="item.icon"></i>
          <span slot="title">{{item.name}}</span>
        </el-menu-item>
      </router-link>
      <sub-menu v-else :data="item" :key="item.id"></sub-menu>
    </template>
  </el-submenu>
</template>

<script>
export default {
  name: "submenu",
  props: {
    data: [Array, Object]
  }
};
</script>

<style lang="scss" scoped>
.el-submenu {
  .el-menu-item {
    padding: 0;
  }
}
</style>

• 效果图