Does anyone know how to assign multiple functions to events like document.onmousedown?

I don't want to overwrite the event handlers placed there by previous script libraries etc.

Essentially, all I want to do is get the mouse state (position, buttons pressed etc) without having to assign an event for it.

M

You can have multiple event handlers for the same event, adding them however you wish (onwhatever="someFunction()", addHandler, addEventListener, etc.).  The won't overwrite each other.  However, different browsers bubble events differently, so you might not know in which order the handlers execute, which creates a remote possibilities of unexpected results.