Create a new file and write text in Javascript

Question

Hello,

I have a website on my own Windows Server 2008 R2. On it a user can write a text on a textarea, hit "Create file" and then:

function myFunction()
{
    var s="";
    var dict = {};
    var data = (s + "").split("");
    [...] // More Javascript stuff here
}

1. There is a default file on my server called default.js which content is just the function above.

2. I would like that we automatically create a copy of this file with a random name and add on the "var s=" statement the text included by the user in the textarea.

Could anyone please tell me which technology is the right one for it? I am not sure if I could/should do it in Javascript or somehow directly on Windows Server.

THANKS A LOT!