Group posts by year with method only

YourPage.vue

<template>
  <Layout>
    <h1>Group by Year via method</h1>
    <ul>
      <li v-for="(items, year) in groupBy($page.allBlogPost.edges, 'createdYear')" :key="year">
        {{ year }}
        <ul>
          <li v-for="item in items" :key="item.id">
            {{ item.title }}
          </li>
        </ul>
      </li>
    </ul>
  </Layout>
</template>

<script>
export default {
  metaInfo: {
    title: 'Hello, world!'
  },
  methods: {
    /*!
    * Group items from an array together by some criteria or value.
    * (c) 2019 Tom Bremmer (https://tbremer.com/) and Chris Ferdinandi (https://gomakethings.com), MIT License,
    * @param  {Array}           arr      The array to group items from
    * @param  {String|Function} criteria The criteria to group by
    * @return {Object}                   The grouped object
    */
    groupBy(arr, criteria) {
      return arr.reduce(function (obj, item) {
        // set the node element as item
        // otherwise we have to use `item.node` everywhere in the code
        item = item.node;
        // Check if the criteria is a function to run on the item or a property of it
        var key = typeof criteria === 'function' ? criteria(item) : item[criteria];
        // If the key doesn't exist yet, create it
        if (!obj.hasOwnProperty(key)) {
          obj[key] = [];
        }
        // Push the value to the object
        obj[key].push(item);
        // Return the object to the next item in the loop
        return obj;
      }, {});
    }
  }
}
</script>

<page-query>
query {
  allBlogPost {
    edges {
      node {
        id
        title
        createdYear: created(format: "Y")
        created
        category {
          title
        }
      }
    }
  }
}
</page-query>

<style>
.home-links a {
  margin-right: 1rem;
}
</style>