Closures...

closure.js

// Global 

const numbers = [1, 2, 3, 4, 5, 6]

const number = (n) => {
  return numbers[n]
}

console.log(number(4))

// Slow (must generate an array at every call only to choose one number)

const number = (n) => {
  const numbers = [1, 2, 3, 4, 5, 6]
  return numbers[n]
}

console.log(number(1))

// Closure

const number = (() => {
  const numbers = [1, 2, 3, 4, 5, 6]
  return (n) => {
    return numbers[n]
  }
})()

console.log(number(2))