Fibonacci Calculator

fibonacci.js

// What a classic!
function fibonacci(n) {
  if(n == 1) return 1
  else if (n == 2) return 1
  else return (fibonacci(n-1) + fibonacci(n-2))
}

// Uses Node's "readline" module for input
// https://nodejs.org/api/readline.html
const readline = require('readline').createInterface({
  input: process.stdin,
  output: process.stdout
})

readline.question("Fibonacci number? ", (userResponse)=> {
  let calculateToNumber = Number(userResponse)
  if(isNaN(calculateToNumber)) console.log("Must be a number")
  else if (calculateToNumber <= 0) console.log("Must be a number greater than 0")
  else console.log(fibonacci(calculateToNumber))
  readline.close()
})