'looks like you solved it'

[a,b], yes.

Square Every Digit

Where are you squaring anything? And next time, please, mark your post as having spoiler content. You also have a double dot there.

• thing is: the arguments are already available (a and b) so why are you using it? (the arguments thing, I mean)
• keep things simple. You don't need that arr thing, just a number that you'll update, then return in the end.

• why do you use arguments? Don't use that... It's old fashion and the best way to do bad things.
• replace isn't a method of Array.prototype => ???
• actually, you're applying replace to the output of push, which is a number... (see MDN documentation) => ???!??

Read the docs of the methods you're trying to use, you're doing it wrong, and why are you using parseInt?