Untitled

<!DOCTYPE html>
<html>
	<head>
		<script type="text/javascript">

			function factorialFun(num1){ // Factorial function
				var result = num1;  // Result


				// While loop
				while (num1 > 1) {
					result = result * (num1-1);
					num1--;

				}
				return result; // result
			}
		</script>
	</head>

	<body>
		<script type="text/javascript">

                // Declare variables and constants
            var num;
            var factorial; // Result
            var BR="<br />"; // Line Break

                // Random num prompt
            num = prompt ("Enter a number from 1 to 20","");
            num = parseInt (num);

            if (num >= 1 && num <= 20) {
				var factorial = factorialFun(num);
				document.write(factorial + BR);
			}

			// thanks user
			document.write("Thank you f!" + BR);

		</script>
	</body>
</html>