Iterative-fib.js

function fib(n) {
    const result = [0, 1];

    for (let i = 2; i <= n; i++) {
        let a = result[i - 1];
        let b = result[i - 2];

        result.push(a + b);
    }

    return result[n];
}

console.log(fib(7));