将字符串转换为数组然后再返回时的 Javascript 问题

Question

我正在尝试解决 Codewars 上的 Javascript 挑战。

等值图是一个没有重复字母的单词，无论是连续的还是非连续的。实现一个函数，确定仅包含字母的字符串是否是等值线图。假设空字符串是等值线图。忽略字母大小写。

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

我的努力如下:

    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;
    }
}

在codewars中我的结果

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

和

的结果

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

这意味着我的解决方案的计算结果始终为假。

如果能给我指明正确方向或指出我的错误，而不是给我解决方案，我将不胜感激，这样我才能更有效地学习。谢谢!

Answer 1

这可能是一个更简单的答案。

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;

}