CodeWards "Consonant please" kata

flatten.js

function flatten(arr) {
  const len = arr.length;
  for (let i = 0; i < len; i++) {
    arr.push(...arr.shift());
  }
  return arr;
}

kata.js

function sortLetters(arr) {
  let flattenedArr = flatten(arr),
      letters = removeNumbers(flattenedArr),
      upperCaseLetters = arrayToUpperCase(letters);
  return upperCaseLetters;
}

function arrayToUpperCase(arr) {
  return arr.map(function(value) {
    return value.toUpperCase();
  });
}

function removeNumbers(arr) {
  let letters = []
  for (let element of arr) {
    if (typeof element == 'string') {
        letters.push(element);
    }
  }
  return letters;
}

function flatten(arr) {
  let flattenedArr = [];
  for (let element of arr) {
    flattenedArr.push(...element);
  }
  return flattenedArr;
}

sortLetters.js

const sortLetters = (arr) => {
  const len = arr.length;
  const vowelIdx = len;
  const consonantIdx = len + 1;

  arr[vowelIdx] = [];
  arr[consonantIdx] = [];

  for (let i = 0; i < len; i++) {
    for (let j = 0; j < arr[i].length; j++) {
      let char = arr[i][j];
      if (typeof char == "string") {
        if (isVowel(char)) {
          arr[vowelIdx].push(char.toUpperCase());
        } else {
          arr[consonantIdx].push(char.toUpperCase());
        }
      }
    }
  }

  arr.splice(0, len);

  return arr;
};

const isVowel = (char) => {
  const vowels = "aeiou";
  return vowels.indexOf(char) >= 0 ? true : false;
};

test.js

sortLetters([[1,"a","H"],[3,"o","s"],[4,"E","i"]]);
sortLetters([["c","A",2],[5,"e","x"],[9,"W","U"]]);
sortLetters([["a",2,"Q"],["I",3,"n"],["E",6,"i"]]);
sortLetters([[9,"i","H"],[0,"U","s"],[1,"o","J"]]);