Enhancement - Any interest in a helper function to show exercise by number?

[seanpoulter]

I've noticed that it takes a bit of fiddling to reproduce issues on specific exercises. Would you accept a PR that adds a showLessonByNumber function like:

/**
 * @param {number} n  The lesson number starting from 1
 */
function showLessonByNumber(n) {
  var item = $(".lesson").get(n - 1);
  if (item) {
    showLesson(item);
  } else {
    throw new Error("Exercise " + (n - 1) + " could not be found.");
  }
}

Since this would be the third spot we're changing the visibility of a lesson, I'd suggest we extract that function as showLesson:

/**
 * @param {Element} lessonElement
 */
function showLesson(lessonElement) {
  var post = $(".post", lessonElement)[0];
  lessonElement.style.visibility = "visible";

  if (post !== undefined) { 
    post.style.visibility = "visible"; 
  } 
}

We could call this function in these two spots as well:

• https://github.com/ReactiveX/learnrx/blob/4a1599c1c751989a01b8df40989d336b1a2c78d4/assets/app/show_answers.js#L18-L21
• https://github.com/ReactiveX/learnrx/blob/4a1599c1c751989a01b8df40989d336b1a2c78d4/assets/app/main.js#L31-L34