JavaScriptでIDごとにオブジェクトの配列をグループ化する方法は？

以下は、JavaScriptでオブジェクトの配列をIDでグループ化するコードです-

例

<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8" />
<meta name="viewport" content="width=device-width, initial-scale=1.0" />
<title>Document</title>
<style>
   body {
      font-family: "Segoe UI", Tahoma, Geneva, Verdana, sans-serif;
   }
   .result {
      font-size: 18px;
      font-weight: 500;
      color: rebeccapurple;
   }
</style>
</head>
<body>
<h1>group the array of objects by Id in JavaScript</h1>
<div class="result">
{ name: 'Rohan', age: 18 }, { name: 'Mohan', age: 20 }, { name: 'Shawn',
age: 18 }, { name: 'Michael', age: 18 }, { name: 'David', age: 20 }
</div>
<button class="Btn">CLICK HERE</button>
<h3>
Click on the above button to sort the above object based on peoples age
</h3>
<script>
   let resEle = document.querySelector(".result");
   let sampleEle = document.querySelector(".sample");
   let BtnEle = document.querySelector(".Btn");
   const people = [
      { name: "Rohan", age: 18 },
      { name: "Mohan", age: 20 },
      { name: "Shawn", age: 18 },
      { name: "Michael", age: 18 },
      { name: "David", age: 20 },
   ];
   let groupBy = (array, key) => {
      return array.reduce((result, obj) => {
         (result[obj[key]] = result[obj[key]] || []).push(obj);
         return result;
      }, {});
   };
   let a = groupBy(people, "age");
   BtnEle.addEventListener("click", () => {
      console.log(a);
   });
</script>
</body>
</html>