string.repeat(n) : 문자 n번 반복
function solution(my_string, n) {
var answer = '';
const l = my_string.length
for (let i=0; i<l; i++){
const item = my_string[i].repeat(n)
answer += item
}
return answer;
}
https://school.programmers.co.kr/learn/courses/30/lessons/120825