odin-js-fundamentals-part-5/10_fibonacci/fibonacci.js

const fibonacci = function(number) {
    if (number == 0) {
        return 0;
    }
    if (number < 0) {
        return "OOPS";
    }
    let a = 1, b = 1;
    let sum = a;
    for (let i = 0;
         i < number - 2;
         i++, (i % 2 == 0) ? a = sum : b = sum) {
        sum = a + b;
    }
    return sum;
};

// Do not edit below this line
module.exports = fibonacci;