function convent(n) {
let neg = false;
let remainder = 0;
let result = "";
if(n<0){
n *= -1;
neg = true;
}
do{
remainder = n % 7;
n = Math.floor(n / 7);
result += remainder.toString();
}while(n);
result = result.split('').reverse().join('');
return neg ? "" + result : result;
}
console.log(convent(7));
console.log(convent(2019));