ASP.NET : Using ClientID in external JavaScript files

In the past year I have been writing a lots of JavaScript code. Mostly because I have been working on same ASP.NET WebForms application for more then 10 months by now. We use JavaScript for things like validation, async HTTP requests etc. To keep our code clean,we try to keep all of our JavaScript in external files. The problem with external JavaScript files is that you cannot use server tags in them, so you cannot obtain ClientID of ASP.NET controls by using <%= control.ClientID %> syntax...