adders.js

// Lets say you have a function that creates adders, for adding two numbers

function makeAdder(firstNumber) {
  return function(secondNumber) {
    return firstNumber + secondNumber;
  };
}

let result

const addFive = makeAdder(5);
result = addFive(3);
console.log(result); // 8

// You don't have to assign it to a temporary variable though
result = makeAdder(10)(20);
console.log(result); // 30