Codewars Kata: 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.

isogram.js

function isIsogram(str){
  
  console.log( 'string: ' + str );
  
  // length of the string
  var stringLength = str.length;
  console.log( 'stringLength: ' + stringLength );
  
  // if the string is empty then it is considered an isogram
  if ( stringLength == 0 ) {
    return true;
  } else {
     
    // make a lowercase version of the string since we ignore case
    var stringLowercase = str.toLowerCase();
    console.log( 'stringLowercase: ' + stringLowercase );
  
    // array containing the individual characters in the lowercase string
    var arrayOfCharacters = stringLowercase.split("");
    
    // loop through the array of characters
    for ( var i = 0; i < stringLength; i++ ) {
      console.log( 'i: ' + i );
    
      // get the character from the array with index i
      var checkChar = arrayOfCharacters[i];
      console.log( 'checkChar: ' + checkChar );
    
      // use reduce to count the number of times the character appears in the array
      var countChar = arrayOfCharacters.reduce( function( n, val ) {
        return n + (val === checkChar);
      }, 0);
      
      console.log( 'countChar: ' + countChar );
      
      // if this character appears more than once in the array then return false
      if ( countChar > 1 ) {
        return false;
      }
    }  
    // otherwise if we get this far then the string is an isogram
    return true;
    
  }

}