<pre class="shiki github-dark shaku"><code>function ObjectGroupBy&lt;T, K extends keyof any&gt;( items: Array&lt;T&gt;, callback: (item: T) =&gt; K): Record&lt;K, Array&lt;T&gt;&gt; { const obj:Record&lt;K, Array&lt;T&gt;&gt; = Object.create(null); items.forEach((item) =&gt; { const key = callback(item) if(key in obj) { obj[key].push(item) } else { obj[key] = [item] } }); return obj}</code></pre>

Most simple solution in the history of mankind!

Object.groupBy() allows us to easily group array items, please try to implement it by yourself. const items = [ { id: 1, kind: 'a', }, { id: 2, kind: …