JavaScriptでハッシュのキーを見つける方法は？

以下は、JavaScriptでハッシュのキーを見つけるためのコードです-

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: 20px;
      font-weight: 500;
   }
</style>
</head>
<body>
<h1>Find keys of a hash in JavaScript</h1>
<div style="color: green;" class="result"></div>
<button class="Btn">DISPLAY</button>
<h3>Click on the above button to display the hash keys</h3>
<script>
   let resEle = document.querySelector(".result");
   let obj = {
      firstName: "Rohan",
      lastName: "Sharma",
      age: 22,
   };
   document.querySelector(".Btn").addEventListener("click", () => {
      resEle.innerHTML += "object keys are " + Object.keys(obj);
   });
</script>
</body>
</html>