I think they could have added a better explanation for this. I looked at the first example and assumed only 'friend' could be the input. Turns out I was wrong

I think they could have added a better explanation for this. I looked at the first example and assumed only 'friend' could be the input. Turns out I was wrong :p But, seriously, what's the difference between this and say, Angular.js? They seem to be solving a similar problem with similar syntax