function isAlt(str) {

    let vowels = 'aeiou'
    let arr = str.split('')
    let arr2 = []
    for (var i=0;i<arr.length;i++)
        { vowels.indexOf(arr[i]) !== -1 ? arr2.push(1) : arr2.push(2) }

    for (  i=1;i<arr.length;i++){
        if (arr[i] == arr[i-1])   { return false }
         }
 return true
}

  isAlt("amazon") // true
  isAlt("apple") // false