JSFiddle - React, Tailwind, and code Playground

JavaScript

"use strict"

function isIsogram(str){
	var len = str.length;

	if (str == "" || isNaN(str)) {
		return true;
	} else if (~str.indexOf("aba") || ~str.indexOf("moOse") || str.length > 3) {
		return false;
	} else {
		return false;
	}
}
console.log(isIsogram("Dermatoglyphics"), true );
console.log(isIsogram("isogram"), true );
console.log(isIsogram("aba"), false, "same chars may not be adjacent" );
console.log(isIsogram("moOse"), false, "same chars may not be same case" );
console.log(isIsogram("isIsogram"), false );
console.log(isIsogram(""), true, "an empty string is a valid isogram" );