Doing Fibonacci, iterative vs. functional

fibonacci.js

// imperative
function fibonacci(n, first = 0, second = 1) {
  while (n !== 0) {
  	console.log(first); // side-effect
  	[n, first, second] = [n - 1, second, first + second]; // assignment
  }
}
fibonacci(10);

// functional
const fibonacci = (n, first = 0, second = 1) => n === 0
  ? ""
  : first + "\n" + fibonacci(n - 1, second, first + second);

console.log(fibonacci(10))

// array with generators
function* fibonacci(n, first = 0, second = 1) {
  while (n !== 0) {
    yield first;
    [n, first, second] = [n - 1, second, first + second] // assignment
  }
}

console.log([...fibonacci(10)]);

// array functional style
const fibonacci = (n, first = 0, second = 1) => n === 0
  ? []
  : [first].concat(fibonacci(n - 1, second, first + second));

console.log(fibonacci(10));