There are a few issues with your code.
1. You cannot declare a function using "Function" because it is not a keyword in JS.
You can use function (remember JS is case sensitive).
2. You cannot start a variable/parameter name with a number. Read more about valid JS
identifier names
here[
^].
3. After you have removed the 1 from the parameter name you'll find out that JS parser
cannot find the variable Name. As pointed out earlier JS is case sensitive, that means name and Name are two different things for JS. Same problem with the function name, a declaration with "account" but usage with "Account".
After you correct these issues you'll find that your code runs.
<!DOCTYPE html>
<html>
<head>
<script type="text/javascript">
function Account(type, num, name, fName, bal) {
this.acctType = type;
this.acctNumber = num;
this.lastName = name;
this.firstName = fName;
this.acctBal = bal;
};
</script>
</head>
<body>
<script>
var BR = "<br/>";
document.write("Account program." + BR);
document.write("This program creates an Account." + BR);
var mySavingsAcct = new Account("S", 1376433,"Dunes", "Sandi", 80.00);
document.write("Thank you!" + BR);
</script>
</body>
</html>