Javascript to run on button with ID

Need some very simple JS code which runs when a button with a specific ID is run *in addition to* the url specified with the button. Use Case:

two buttons on a download app page - one opens Google Play Store in a new window, the other opens Apple App Store in a new window.
The JS then needs to run which takes the user from the download app page to a 'How to use' page on the main site. this url is set in the JS for each ID.