Node module to provide the correct article for words starting with vowels

article.js

/* 
 TODO: * An article that starts a sentence should be capitalized.
       * A more comprehensive list of subtleties like "a useful", "a once", "an hour", "an historical"
       * Tests
*/
exports.article = function(text) {
  var vowels = 'aeiou';
  var an_exceptions = ['eucalyptus', 'eunuch', 'euphemism', 'euphemistic', 'euphonium', 'euphoric', 'european', 'once', 'one', 'onesie', 'union', 'unique', 'unison', 'united', 'useful', 'utopia', 'utopic', 'user', 'unicorn'];
  var a_exceptions = ['hour', 'historical', 'honorable', 'honourable'];
  if (a_exceptions.indexOf(text) != -1 || (vowels.indexOf(text.charAt(1)) == -1 && an_exceptions.indexOf(text) == -1)) {
    return 'an';
  }
  else {
    return 'a'; 
  }
}