I've seen a few topics on "~てやる" here (I do apologise in advance if this question overlaps too much with any previous answered posts), but I have a specific question regarding the phrase "やってやる".
I was told by a fellow Japanese learner that "やってやる" is a casual way of saying "I'll do it for you" so the nuance is + "for someone". However, my textbook only lists the following definitions:
To do it/ to give it a go
With no mention of doing something specifically "for someone".
Is the nuance indeed doing something "for someone" or is it just "I'll do it" regardless of whether your doing something for someone or not?