currying-1.js

function realSum(a, b) {
  return a + b;
};

function sum(a, b) {

  return b ?
    realSum(a, b) :
    function(b) {
      // This anonymous function has access to variable `a` via closure
      return realSum(a, b);
    }
}

console.log(sum(5, 3)); // 8

var sum5 = sum(5);
console.log(sum5(4)); // 9

var sum3 = sum(3);
console.log(sum3(4)); // 7