New to JS; how do I make a script to receive an argument through a URL?

New to JS; how do I make a script to receive an argument through a URL?

I am new to JavaScript and I am trying to implement it into a website like
this.
A person wants to download a file. They click on a link, which takes them
to another HTML file with the download link, a keyword, and an
advertisement. So they would be on http://website.com/randompage and they
would click on a link to download a file which would take them to
website.com/download.html?keyword=text?file_url=http://website.com/file.txt
If website.com/download.html could accept 2 parameters into an imbedded
JavaScript (or a seperate file, whichever works better). Then the
download.html would show a link to download the file at variable file_url
and would display the keyword from variable keyword. Then an ad would be
displayed according to the keyword (my ad service does that for me). Is
this possible to do? I would like a sample script, if possible. The ad
code can be left out (I already have that part). Thanks in advance :)