first-class.js

function times(first, second) {
  return first * second;
}

console.log(times(3, 4)); // 12

console.log(times(10, 50)); // 500

console.log(times); // function () {}

function fillFirst(func, first) {
  return function (second) {
    return func(first, second);
  }
}

var times10 = fillFirst(times, 10);

console.log(times10(100)); // 1000

console.log(times10(3)); // 30