Fun (help) with tiles!

Greetings, all. I’m currently working on a tile based game, but that’s pretty much where i’ve hit the wall. Does anybody know of a good way to load and store external bitmap images so I can use them as tiles? Currently it’s set up so the bitmap loads whenever the tile gets created, but that ended up being way to slow in a browser. If there was a way where I could just load each bitpmap once somehow, and use the bitmap data whenever the appropriate tile was needed, that would be great. One other option I was trying to work with was to import them all into the library, but then they would each have to have their own specific class, which is not good. Any advice would be great! Thanks