All events are 'if' block. There's generally no need to specify else.
You can add an system condition else, which states that the event will only run if the previous event did not run in and given tick. Also events run top to bottom. The whole sheet is processed every tick, so if your idle animation event is above your other two, it can normally run every tick and will get overwritten by the other animations when those events activate.
Else is normally used in cases such as toggles, where one event says if x, then change to y, and the following event says if y, then change to x. Since there will both be true, the toggle can never change to y. This can be solved with the else condition.
You can use JavaScript directly in Construct 3, although in my opinion that kind of defeats the whole point of C3 in the first place. One of the main selling points for me was how logically intuitive the event system was.