Show Objects Array As a Nested List

Question

In my vue app, I have an array of objects which I want to render as a list. Within each object, there is a 'parent' property which contains info about who the parent is thereby giving us a hierarchical data structure. However, I am unable to show this hierarichal list. I tried creatin a tree by transforming the data but my code seems bugged.

You can see my attempted version here: http://jsbin.com/pewusiyete/edit?html,js,console,output

Code

<!DOCTYPE html>
<html>
<head>
  <meta charset="utf-8">
  <meta name="viewport" content="width=device-width">
  <title>JS Bin</title>
</head>
<body>

  <div id="app">
    <ul>
      <li v-for="item in list">
        <a v-bind:href="item.value">{{item.label}}</a>
      </li>
    </ul>
    {{tree}}
  </div>
<script src="https://cdnjs.cloudflare.com/ajax/libs/vue/2.0.3/vue.js"></script>
<script>
    new Vue({
        el:'#app',
        data:{
            list:[
   {
      "label":"Parks & Gardens",
      "type":"place",
      "value":"parks-gardens",
      "id":"0CNYF4qh0aaYi2XLGCfG"
   },
   {
      "label":" Art & Craft",
      "type":"product",
      "value":"art-craft",
      "id":"4TfXwraLAJX9K5WeIBT5"
   },
   {
      "label":"Monuments",
      "type":"place",
      "value":"monuments",
      "id":"4mVxy4QEplxTnf6NwpIf"
   },
   {
      "label":"Books",
      "type":"book",
      "value":"books",
      "id":"4oVqbEDhPSYqaTDn4xMV"
   },
   {
      "label":"Sports Academies",
      "type":"place",
      "value":"sports-academies",
      "id":"H7GkAF0Hfdu3OoHBYyQY"
   },
   {
      "label":"Store",
      "type":"place",
      "value":"store",
      "id":"Ki4YjRNe4HmZWOCOpg9K"
   },
   {
      "label":"Tennis Academies",
      "parent":"sports-academies",
      "type":"place",
      "value":"tennis-academies",
      "id":"N89adEZwHfSGMQiq1R5f"
   },
   {
      "label":"Toy Stores",
      "type":"place",
      "parent":"stores",
      "value":"toy-stores",
      "id":"Oj6QgO0S0Z6AFHvrr2ZH"
   },
   {
      "label":"Electronics",
      "type":"product",
      "value":"electronics",
      "id":"UuztFKZrsw3vcciKaj8k"
   },
   {
      "label":"Tech",
      "type":"product",
      "value":"tech",
      "id":"WuqiVSXxmlCCQ5usAUNZ"
   },
   {
      "label":"Book Stores",
      "type":"place",
      "parent":"stores",
      "value":"book-stores",
      "id":"ZmXlJ12jJROGeHjYcwOT"
   },
   {
      "label":" Online Stores",
      "type":"commerce",
      "value":"online-stores",
      "id":"cIRSVPcqSDr6WfuRe4OX"
   },
   {
      "label":"Play Areas",
      "type":"place",
      "value":"play-areas",
      "id":"fEk3dcKprq9Hd8rSgiG3"
   },
   {
      "label":"Toys",
      "type":"product",
      "value":"toys",
      "id":"rJTpw2V9apxe9jQjLTOS"
   },
   {
      "label":"Stores",
      "type":"place",
      "value":"stores",
      "id":"ZmXlJ12jJROGeHjYcwOH"
   }
]
        },
        computed: {
          newitem: function () {
            return this.list.reduce(function(p,c) {
              p[c.value] = c;
              c.children = [];
              return p;
              }, {}); 
          },
          tree: function () {
            return this.list.reduce(function(p,c) {
              console.log(c.parent)
            if (c.parent = 'undefined') {
              p = c;
            } else {
              newitem[c.parent].children.push(c);
            }
            return p;
            }, {});
          }
        }     
    });
</script>
</body>
</html>

tony19 · Accepted Answer · 2022-07-16 01:16:11Z

There's a few things wrong with your code, I won't go into too much detail, but at a high level:

if (c.parent = 'undefined') should probably be if (c.parent === undefined).
newitem[c.parent].children.push(c) should probably be this.newitem[c.parent].children.push(c), but even then you shouldn't mutate computed properties.
I think just overall you are not structuring your menu items properly.

First you will need to transform the flat list of items into a tree structure. Then you will need to use recursive components in order to render such a tree.

Here's an example:

const MenuList = {
  name: 'menu-list',
  template: '#menu-list-template',
  props: ['items'],
};

new Vue({
  el: '#app',
  components: {
    MenuList,
  },
  data: {
    list: [
      {
        "label": "Parks & Gardens",
        "type": "place",
        "value": "parks-gardens",
        "id": "0CNYF4qh0aaYi2XLGCfG"
      },
      {
        "label": " Art & Craft",
        "type": "product",
        "value": "art-craft",
        "id": "4TfXwraLAJX9K5WeIBT5"
      },
      {
        "label": "Monuments",
        "type": "place",
        "value": "monuments",
        "id": "4mVxy4QEplxTnf6NwpIf"
      },
      {
        "label": "Books",
        "type": "book",
        "value": "books",
        "id": "4oVqbEDhPSYqaTDn4xMV"
      },
      {
        "label": "Sports Academies",
        "type": "place",
        "value": "sports-academies",
        "id": "H7GkAF0Hfdu3OoHBYyQY"
      },
      {
        "label": "Store",
        "type": "place",
        "value": "store",
        "id": "Ki4YjRNe4HmZWOCOpg9K"
      },
      {
        "label": "Tennis Academies",
        "parent": "sports-academies",
        "type": "place",
        "value": "tennis-academies",
        "id": "N89adEZwHfSGMQiq1R5f"
      },
      {
        "label": "Toy Stores",
        "type": "place",
        "parent": "stores",
        "value": "toy-stores",
        "id": "Oj6QgO0S0Z6AFHvrr2ZH"
      },
      {
        "label": "Electronics",
        "type": "product",
        "value": "electronics",
        "id": "UuztFKZrsw3vcciKaj8k"
      },
      {
        "label": "Tech",
        "type": "product",
        "value": "tech",
        "id": "WuqiVSXxmlCCQ5usAUNZ"
      },
      {
        "label": "Book Stores",
        "type": "place",
        "parent": "stores",
        "value": "book-stores",
        "id": "ZmXlJ12jJROGeHjYcwOT"
      },
      {
        "label": " Online Stores",
        "type": "commerce",
        "value": "online-stores",
        "id": "cIRSVPcqSDr6WfuRe4OX"
      },
      {
        "label": "Play Areas",
        "type": "place",
        "value": "play-areas",
        "id": "fEk3dcKprq9Hd8rSgiG3"
      },
      {
        "label": "Toys",
        "type": "product",
        "value": "toys",
        "id": "rJTpw2V9apxe9jQjLTOS"
      },
      {
        "label": "Stores",
        "type": "place",
        "value": "stores",
        "id": "ZmXlJ12jJROGeHjYcwOH"
      }
    ]
  },
  computed: {
    treeList() {
      // Deep clone the list and add a children property with empty array value to each item
      const items = this.list.map(item => Object.assign({}, item, { children: [] }));
      
      // Organize items into a map keyed by item value for easy lookup
      const byValue = new Map(items.map(item => [item.value, item]));
      
      // Top level will contain the items which do not have a parent
      const topLevel = [];
      for (const item of items) {
        // Look up the parent item if there is one
        const parent = byValue.get(item.parent);

        if (parent) {
          // Append the item into the parent's children array
          parent.children.push(item);
        } else {
          // The item has no parent
          topLevel.push(item);
        }
      }
      
      return topLevel;
    }
  }
});

<script src="https://rawgit.com/vuejs/vue/dev/dist/vue.js"></script>

<div id="app">
  <menu-list :items="treeList"></menu-list>
</div>

<script type="text/x-template" id="menu-list-template">
  <ul v-if="items.length">
    <li v-for="item of items">
      <a :href="item.value">{{ item.label }}</a>
      <menu-list :items="item.children"></menu-list>
    </li>
  </ul>
</script>

Not that Map is not supported in older browsers (read: IE) and rwquires a polyfill in those.
Thanks so much. This works perfectly. I took some time to understand my mistakes and the code you've provided. But it makes perfect sense!
I have two more confusions here. 1) When the nested list is created, is it possible to assign two different classes to the parent <ul> and to the child <ul> How do I do that? 2) Is it possible to sort the parent list alphabetically?

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