The question/qengine.js is too old and we need to convert it to an AMD module. After checking the new code from question/bank/previewquestion/amd/src/preview.js, I think that question engine should be a general amd module instead of a part of preview.js, because it is using on other places such as quiz attempt.

I have created 2 modules to split qengine.js to 2 separate part:

1. lib/amd/src/scroll_manager.js:

The scroll function in qengine.js has not working for along time. The root cause it the theme changing. The windows is not the current scrolling element anymore. I have fixed this feature to make it work again for both Boost and Clean theme.

As Tim suggestion, I have remove the scrollPos parameter and using a generic code to add it in redirect()

I have remove the save_scroll_action(), and replace with a new function: initLinksScrollPos(). If a link has 'data-save-scroll' attribute = true, when we click on the link, the js code will add mdlscrollto parameters with the current scroll position into the link and open the link.

I have added the scroll function to the "Try another question like this one" button. 

2. question/amd/src/question_engine.js

I have remove the hashtag in form action in init_submit_button() to make the scroll smoother.

I have checked the usage of the old code across the site. It has removed some where because it has been working for along time. I just found some pages to test the old function:

Quiz attempt

Preview question

Other question/quiz pages should work normally.

Original Description:

This is some old JavaScript in the question engine.

I think that the M.core_scroll_manager.save_scroll_action bit is generally useful so should be converted to a module like core/scroll_manager. Looks like there is scope to improve the code there, for example:

1. Rather relying on an event handler being added to individual links and buttons, perhaps make it use a data attribute (e.g. data-save-scroll) and have a single delegated event handler on body.
2. Get rid of the "Assumes that the link already contains at least one URL parameter." limitaion.
3. Hopefully it is now save to remove the IE-specific hack (but this needs to be tested).

Then, M.core_question_engine should become an AMD module in core_question.

Just to note that current best practice for JavaScript is:

• ES6 module syntax
• No third-party JS libraries at all unless really needed.

Apparently https://github.com/moodle/moodle/blob/master/lib/amd/src/toast.js is good recent example.

I think that the historic entry-point into this code are the API

• page->requires->js_module('core_question_engine');
• page->requires->js_init_call('M.core_question_engine.init_submit_button',
  array($attributes['id'], $qa->get_slot()));

And https://docs.moodle.org/dev/Using_the_question_engine_from_module#Handling_scrollpos

We need to work out how the normal Moodle deprecation rules apply to this.