Is the Word an Isogram?

An isogram is a word that has no duplicate letters. Create a function that takes a string and returns either true or false depending on whether or not it's an "isogram".

Examples

isIsogram("Algorism") ➞ true

isIsogram("PasSword") ➞ false
// Not case sensitive.

isIsogram("Consecutive") ➞ false

Notes

• Ignore letter case (should not be case sensitive).
• All test cases contain valid one word strings.