Whatever JavaScript a web page runs, shouldn't it be driven by some kind of event though? Rather it be the "onLoad" event itself, or the user clicking/hovering

Whatever JavaScript a web page runs, shouldn't it be driven by some kind of event though? Rather it be the "onLoad" event itself, or the user clicking/hovering/changing something, etc. In a real use case setting, you wouldn't have users load a web page and then somehow arbitrarily execute JavaScript code directly, without any particular event firing. So why wouldn't you test through the relevant events?