Create Isogram.js

Isogram.js

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+/**
+*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
+**/
+
+/**
+*Set's size should be equal to string length
+**/
+function isIsogram(str){
+  const set = new Set();
+  for(let i=0;i<str.toLowerCase().length;i++) {
+    set.add(str.charAt(i));
+  }
+  return str.length === set.size;
+}