Make a wipe in javascript that reveals a picture with a mask.

I've been trying to come up with a script to accomplish this task. I've got a script that can make an circle object move to follow the cursor. I've limited the movement from left to right, which is perfect. I've got a second script that creates a box in javascript that can mask a movie in Animate. Just can figure out how to get the two scripts to cooperate. I'm sure there is some Javascript magic that I just can't figure it out. Please help.