Given an array of words and a number k, your task is to return an array with length k

Given an array of words and a number k, your task is to return an array with length k where the ith element is the number of unique prefixes with length i + 1 among the given words (including only words that are at most i characters long).

function solution(words, k) {

  const rtnArr = new Array(k);

  const prfArr = [];

  for(let i = 0; i < k; i++){

    const prArr = words.map(item => item.length >= i+1 ? item.substring(0, i+1) : "");

    const uniqueArr = prArr.filter((value, index, self) => {

    return value && self.indexOf(value) === index;

  });

    rtnArr[i] = uniqueArr.length;

  }

  return rtnArr;

}