<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; { // Your code here //return null when empty object const result:any=Object.create(null); // for of loop to check if items are iterable for(let obj of items){ const keyName=callback(obj); if(result[keyName]){ result[keyName].push(obj); }else{ result[keyName]=[obj] } }; return result;}</code></pre>

group by polyfill

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: …