A very basic question

[Diversions]

I have just put together my first retail site and since inventory fluctuates constantly, I need to be able to advise shoppers when items are temporarily unavailable. Rather than going through a thousand unsorted pages, I thought I could do this easier with javascript if I had a .js file set up for each product code and then I wouldn't have to go through each page in the site. Is this possible with Javascript? If so, what code would I put on the page where I want it to show and what code would I place in the .js file?
I tried mucking about on my own but got lost and confused.

I am obviously pretty new and apologize for the very elementary question.

[Twey]

You'd do better with a database and a server-side script.

[Diversions]

Okay, thanks!