Here, my first comment got deleted. I asked the OP if he read the documentation he found and what wasn't clear... Any reason to delete that comment?

Obviously the documentation is quite clear about it. 

The comment: *[What is the purpose of thisArg in .forEach?](https://stackoverflow.com/questions/34556558/javascript-foreach-what-is-the-purpose-of-thisarg?noredirect=1#comment56858361_34556558)*