Custom Form Javascript - Multiple Task

I have a form on my site which runs a javascript to redirect visitors to 4 different pages based on zip code range and yes/no button selected. Currently the javascript redirects visitors to other urls and I need someone to change the redirect to open in a new tab (without triggering pop-up blockers). I also want to implement another javascript code (which I have) to run on the original page which will also use the zipcode imput to run a script (i have). The person who takes this job would have to edit my existing javascript without affecting the functionality and implement another existing javascript to work with my form and in conjunction with my existing script. ***VERY IMPORTANT*** The code would have to be tested in different browsers to ensure functionality cross-browser.