(For point 1) Got it, from now on variables will be declared with let. I don't understand what is "use strict"; maybe you can explain it.
(For point 2) I was testing to see if reversedWord printed the desired output in the Console, forgot to remove it after finishing the program. I also don't understand what 'O(N^2)' and 'O(N)' is, but +=-ing an empty string is a great idea, why didn't i think of that.
I see you're a Walking Dead fan