if else statement in javascript.html

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>if else statement</title>
</head>
<body>
    <script>
        var a = prompt("enter your age");
        if((a == 18))
        document.write("You are eligible to vote");
        else
        document.write("You are not eligible to vote");
  // 2nd example
   var b = prompt("Enter Your Age");
   if((b == 10))
     document.write("Your are Child")
   if((b==20))
   document.write("Yor are Young");
if((b ==30))
document.write("Yor are old");


  
  
  </script>
</body>
</html>