<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) { // Your code here let newObj = Object.create(null); for(let item of items) { let targetK = callback(item); if (!(targetK in newObj)) { newObj[targetK] = new Array(); } newObj[targetK].push(item); } return newObj}const items = [ { id: 1, kind: 'a', }, { id: 2, kind: 'b', }, { id: 3, kind: 'a', }]const groups = ObjectGroupBy(items, ({kind}) =&gt; kind)console.log( ObjectGroupBy( [0, 1, 2, 3, 4, 5], (item) =&gt; item % 2 === 0 ? 'even' : 'odd' ))</code></pre>

注意 null-prototype objects 初始化：Object.create(null)

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: …