Javascript Redirecting Form + Prevention System

Part I

Hello, I would like to create a JavaScript-based login system, where there would be a login page for example (login123.com) with only one single field form, then the user would type something in that form and they would submit it, then the script would redirect the user to the forms value + .com, for example, if the user inputs (test123) and submits the form then the script would redirect him to (test123.com).

Part II:

I also need a security system for the protected site where the script would check if the user is coming from a specific page URL (the form website from part I, login123.com) and if not then it would prevent him from viewing the content of the protected site and would redirect him to google.

-Thanks