JavaScrip

Have a problem with the following Java Script example.

var newCustomer;
var establishedCustomer;

newCustomer = window.prompt('New customer','Type number 1 here','');
document.write('WELCOME - WE WILL SET UP YOUR ACCOUNT DETAILS NOW'+'
');
establishedCustomer = window.prompt('Established customer','Type number 2 here');
document.write('SHOP UNTIL YOU DROP');

Need help to stop the program when either 1 or 2 is imput into the solution or if after 2 attempts the program does not produce any output.