Design a javascript program that asks the user for a username with at least eight characters, beginning with a letter and including at least one digit. Next, write a validation loop to ensure that these conditions have been met, and continue to prompt the user until a valid username has been entered. (Hint: You can use the functions substring(),
isLetter(), and isNumeric() to validate the input.) Use Notepad to create the program, and save the ?le as usernameValidator.html.