dummy.html

<!DOCTYPE html>
<html lang="en">
<head>
   
    <title>My Dom Project</title>
</head>
<body onload="alert('Hello world')">
    <h1> My heading</h1>
   
    <form id="form">
      <label for="number label" > Car  :</label>
      <input type="text" id="TextBox">
      

      <input type="button" value="Check Car" >
   
    </form>

   
</body>

<script type="text/javascript">

class Car {
  constructor(brand) {
    this.carname = brand;
  }
  present() {
    return 'I have a ' + this.carname;
  }
}
class Model extends Car {
  constructor(brand, mod) {
    super(brand);
    this.model = mod;
  }
  show() {
   
    alert(this.present() + ', it is a ' + this.model);
    // return this.present() + ', it is a ' + this.model;
  }
}
function brandd(){

    var cuBrand = document.getElementById("TextBox").value;
    return cuBrand;

}

let myCar = new Model(brandd(), "Mustang");
// document.getElementById("demo").innerHTML = myCar.show();


console.log(myCar.present());
console.log(myCar.show());


</script>


</html>