All tasks work as requested. I have just some small improvements/simplifications:
Task 1: Basing the condition on the button text feels a bit inflexible. I recommend using the class (and also change it accordingly).
Task 2: Good idea to also test for the uppercase letters. You could use a switch statement instead of the nested if...else. Another possible simplification would be to call drawCircle after the statement and only change the x/y value inside.
Task 3: You could replace event.currentTarget with just buttonBar.