Isograms.js

// 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.

// Example: (Input --> Output)

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

// isIsogram "Dermatoglyphics" = true
// isIsogram "moose" = false
// isIsogram "aba" = false

function isIsogram(str){
  
  return !str || str.toLowerCase().split('').every((el, i, str) => str.indexOf(el) === i)
  
}

//different approach 

function isIsogram(str){
	return new Set(str.toUpperCase()).size == str.length;
}

//different approach

function isIsogram(str){
  var i, j;
  str = str.toLowerCase();
  for(i = 0; i < str.length; ++i)
    for(j = i + 1; j < str.length; ++j)
      if(str[i] === str[j])
        return false;
  return true;
}