How can I make var a = add(2)(3); //5 work?

Question

I want to make this syntax possible:

var a = add(2)(3); //5

based on what I read at http://dmitry.baranovskiy.com/post/31797647

I\

Answer 1

Here we use concept of closure where all the functions called inside main function iter refer and udpate x as they have closure over it. no matter how long the loop goes , till last function , have access to x.

function iter(x){    
return function innfunc(y){
//if y is not undefined
if(y){
//closure over ancestor's x
x = y+x;
return innfunc;
}
else{
//closure over ancestor's x
return x;
    }
  }
}

iter(2)(3)(4)() //9 iter(1)(3)(4)(5)() //13