Menu Item Select On Page Load - Actual Element (a Table) To Set The Background Doesn't Exist

I have a menu that I have constructed through HTML/CSS/JavaScript. Javascript handles the mouseover and mouseout events to set the background of the menu item/table element with an image. It works great. What my issue is right now is that when the user loads the Home page, I want that to have the background of the item already set. I had a function to do this with a switch clause in a separate javascript file. This function was called immediately (left it outside of any functions so it would execute first). But I'm getting an error because the actual element (a table) to set the background doesn't exist yet.