Generate the Fibonacci sequence in JavaScript

The Fibonacci sequence is a series of numbers in which each number is the sum of the two preceding ones, starting with 0 and 1. To generate the Fibonacci sequence using code, you can use either a recursive or an iterative approach.

Iterative approach

The simplest way to calculate the Fibonacci sequence is to use an iterative approach. You can use a for loop to generate the sequence up to the nth term, using an array to store the values.

const fibonacci = n => {
  let fib = [];
  for (let i = 0; i < n; i++) {
    if (i <= 1) fib.push(i);
    else fib.push(fib[i - 1] + fib[i - 2]);
  }
  return fib;
};

fibonacci(6); // [0, 1, 1, 2, 3, 5]

Recursive approach

The recursive approach is more elegant and concise, but it can be less efficient due to the overhead of function calls. Instead of a loop, it uses a function that calls itself with a smaller input until it reaches the base case of either n = 1 or n = 2, at which point it returns the corresponding array.

const fibonacci = n => {
  if (n === 1) return [0];
  if (n === 2) return [0, 1];
  const fib = fibonacci(n - 1);
  return fib.concat(fib[fib.length - 1] + fib[fib.length - 2]);
};

fibonacci(6); // [0, 1, 1, 2, 3, 5]