Avoiding explicit promise construction antipattern

## not-bad-code.js
function getUserDetail(username) {
  if (userCache[username]) {
    return Promise.resolve(userCache[username]);
  }

  // Use the fetch API to get the information
  return fetch('users/' + username + '.json')
    .then(function(result) {
      userCache[username] = result;
      return result;
    })
    .catch(function() {
      throw new Error('Could not find user: ' + username);
    });
}