<pre class="shiki github-dark shaku"><code>/** * @template T * @template { keyof any } K * @param { Array&lt;T&gt; } items * @param { (item: T) =&gt; K } callback * @returns { Record&lt;K, Array&lt;T&gt;&gt; } */function ObjectGroupBy(items, callback) { let res = Object.create(null) for(let item of items){ const fnRes = callback(item) if(res[fnRes]){ res[fnRes].push(item) }else{ res[fnRes] = [item] } } return res}</code></pre>

O(n)

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: …