Steps: The fibonnaci sequence is the integer sequence where the first two terms are 0 and 1. After that, the next term is defined as the sum of the previous two terms. Hence the nth term is sum of n-1 term and n-2 term.

function fibonnaci(num) {
    if (num < 2) {
        return num;
    } else {
        return fibonnaci(num - 1) + fibonnaci(num - 2);
    }
}

let arr = [];
for(let i = 0; i < 10; i++) {
    arr.push(fibonnaci(i));
}

console.log(arr);

References: