JavaScriptでオブジェクトを作成してそのプロパティにアクセスするにはどうすればよいですか？

以下は、オブジェクトを作成し、JavaScriptでそのプロパティにアクセスするコードです-

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: 20px;
      font-weight: 500;
   }
</style>
</head>
<body>
<h1>Hoisting in JavaScript</h1>
<div style="color: green;" class="result"></div>
<button class="btn">CLICK HERE</button>
<h3>
Click on the above button to create and access a object
</h3>
<script>
   let btnEle = document.querySelector(".btn");
   let resEle = document.querySelector(".result");
   let obj = {
      firstName: "Rohan",
      lastName: "Sharma",
      welcome() {
         return "Welcome " + this.firstName + " " + this.lastName;
      },
   };
   btnEle.addEventListener("click", () => {
      resEle.innerHTML = "obj.firstName = " + obj.firstName + "<br>";
      resEle.innerHTML += "obj.lastName = " + obj.lastName + "<br>";
      resEle.innerHTML += "obj.welcome() = " + obj.welcome() + "<br>";
   });
</script>
</body>
</html>