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

function add(x){
  return function(y){
    return x+y
  }
}

First-class functions and closures do the job.

Answer 2

ES6 syntax makes this nice and simple:

const add = (a, b) => a + b;

console.log(add(2, 5)); 
// output: 7

const add2 = a => b => a + b;

console.log(add2(2)(5));
// output: 7

Answer 3

I came up with nice solution with closure, inner function have access to parent function's parameter access and store in its lexical scope, when ever we execute it, will get answer

    const Sum = function (a) {
        return function (b) {
            return b ? Sum(a + b) : a;
        }
    };

    Sum(1)(2)(3)(4)(5)(6)(7)() // result is 28
    Sum(3)(4)(5)() // result is 12
    Sum(12)(10)(20) // result is 42

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Answer 4

const add = a => b => b ? add(a+b) : a;

console.log(add(1)(2)(3)());

Or (`${a} ${b}`) for strings.