Javascript problems when converting a string to an array and then back again

Question

I am trying to solve a Javascript challenge on Codewars.

An isogram is a word that has no repeating letters, consecutive or non-consecutive. Implement a function that determines whether a string that contains only letters is an isogram. Assume the empty string is an isogram. Ignore letter case.

isIsogram( "Dermatoglyphics" ) == true
isIsogram( "aba" ) == false
isIsogram( "moOse" ) == false // -- ignore letter case

My effort is below:

    function isIsogram(str) {
    var arr = str.split("");
    var seen = {};
    var out = [];
    var length = arr.length;
    var j = 0;
    for(var i = 0; i < length; i++) {
         var item = arr[i].toLowerCase;
         if(seen[item] !== 1) {
               seen[item] = 1;
               out[j++] = item;
         }
    }
    console.log(out.toString.toLowerCase);
    console.log(str.toLowerCase);
    if (out.toString.toLowercase === str.toLowerCase) {
     return true;
    }
    else {
      return false;
    }
}

In codewars the result of my

console.log(out.toString.toLowerCase); is undefined 

and the result of

console.log(str.toLowerCase); is [Function: toLowerCase].

This means my solution always evaluates to false.

I would appreciate any help to point me in the right direction or highlight my errors instead of giving me the solution so I can learn more effectively. Thanks!

Answer 1

This may be a simpler answer.

function isIsogram(str){

  // Turn all letters of the string to lower case and split it into an array. 

  var letters = str.toLowerCase().split('');
  var checkLetters = [];
  
  /* Check to see if the letter appears in the checkLetters array.
     If the letter is not already in the array it will push the letter into it. */

  letters.forEach(function(letter) {
    if(checkLetters.indexOf(letter) === -1) {
      checkLetters.push(letter);
    }
  });

  /* Now we have two arrays. If the letters array has non-duplicate letters then 
     it will be the same length as the checkLetters array. If not, the checkLetters array
     will be shorter. */

  /* Return true or false depending on whether the lengths of both arrays are equal */
    
  return letters.length === checkLetters.length ? true : false;

}