How would you prevent one movie clip playing while another is still playing in a parent animation?

Hi everyone,

I'm just getting started with Adobe Animate and I've created an interface which has three sub menus which transition in/out depending on user interaction.
So, I click on option A and its sub items transition out of that to be viewable and clickable.
I then click on option B and option A's sub items transition back in while option B's sub items transition out to be clicked etc.

However, if I click on them in quick succession - ie, before the option A's sub items have fully transitioned out - then B's items will appear while A's are still in transition.

I feel like I need to set a parent variable which denotes when a transition is still happening and only allows interaction once any transition is complete. But my initial attempt to set a variable at the top level and then change it in a movie clip's javascript returned a variable definition error - likely a scope issue?

I'm going to keep trying things, but any thoughts on this would be really greatly appreciated!
Thanks in advance - my first post here, but I've read a fair few threads so far!

Notes: Project is HTML 5 Canvas, including three menu items created as movie clips to allow scale transitions and control interactions with sub items.
Menu toggling is controlled by script in the main timeline action layer, whereas sub-item interactions are controlled with script in the movie clips' action layers.