SOURCE

function fibo(n){
    if(n===0) return 0;
    if(n===1) return 1;
    let pre = 0;
    let curr = 1;
    for(let i =2;i<=n;i++){
        const next = pre+curr;
        pre = curr;
        curr= next
    }
    return curr
}

console.log(fibo(10))