old_contents: const assert = require('assert');
  
  const countVowels = str => Array.from(str)
    .filter(letter => 'aeiou'.includes(letter)).length;
  
  console.log(countVowels('abcdefghijklmnopqrstuvwxyz')); // 5
  console.log(countVowels('December')); // 3
  console.log(countVowels('xxx')); // 0
  
  
  
new_contents: const assert = require('assert');
  
  const countVowels = str => Array.from(str)
    .filter(letter => 'aeiou'.includes(letter)).length;
  
  console.log(countVowels('abcdefghijklmnopqrstuvwxyz')); // 5
  console.log(countVowels('December')); // 3
  console.log(countVowels('xxx')); // 0
  
  const a1 = "vowels";
  const r1 = "array";
  
  assert(r1);
  
subject: edit input for example