JS Bin// source http://jsbin.com/diqumox

jsbin.diqumox.js

// Count the number of vowels in a string using just var
function count(targetString){
  var characters = ['a', 'e', 'i', 'o', 'u'];
  var number = 0;
  for (var i = 0; i< targetString.length; i++){
    if(characters.includes(targetString[i])){
      number++
    }
  }
  return number;
}

console.log(count('aeiobzxceiaipbiox'));

// Count the number of vowels in a string using const and let
function count(targetString){
  const characters = ['a', 'e', 'i', 'o', 'u'];
  let number = 0;
  for (var i = 0; i< targetString.length; i++){
    if(characters.includes(targetString[i])){
      number++
    }
  }
  return number;
}

console.log(count('aeiobzxceiaipbiox'));