Base 7

LeetCode題目: 504. Base 7

My solution:

/**
 * @param {number} num
 * @return {string}
 */
let convertToBase7 = num => {
    if(num === 0) return '0';
    let negative = num<0, res = '';
    num = Math.abs(num);
    while(num !== 0) {
        res = num%7 + res;
        num = Math.floor(num/7);
    }
    return (negative ? '-' : '') + res;
};