What does y(x) do in this arrow funtion

I do not get what y(x) in the third line does

var x = 5;

var y = 1;

( (x, y)=>(y => y(x) + 1)(x => x * 3 + y) ) (x, y);

// returns 17 

I suspect that the f(x) calls the arrow function on the right.

>Solution :

That:

(y => y(x) + 1)

is a lambda (an anonymous function) that takes a function y as an argument.

Its argument is:

(x => x * 3 + y)

Thus it is the same as:

((x => x * 3 + y)(x) + 1)
((x*3)+y)+1

and all this is part of a function ((x, y)=> …) which is applied with the arguments (5,1).