Javascript to "stop" the script

Job ID: 39036276

Budget: €8 – €30 EUR

I need to manage a free script, because I need to implement a check point.
Only use old/standard javascript code (v.1.0) to be compatible with older browsers. No jQuery.

The script is this
https://codepen.io/maheshambure21/pen/RrXaLX

It works. Click on ‘next’ to go to the next screen.
On the first <fieldset>, when user click on NEXT, I need to
- check if all field (or one) is empty
- if is empty, stop the animation

When issue is solved, clicking again on NEXT second <fieldset> could be load.

No upfront. No payment before successful completion of all tests.
Source-code required for test.
Very low available budget (10 euro)
Related categories: JavaScript CSS HTML5 HTML jQuery / Prototype