Can someone tell me why it says "Cannot read property childNodes of null"?

Question

I've been staring at this for a long time but as far as I can tell my "par" variable is completely valid.
https://code.sololearn.com/WI0DCYccz8Ib/?ref=app

Answer 1

Some extra info that may help
https://code.sololearn.com/WcdoF4PGPyDC/#html

Answer 2

The document is not ready while executing the code. Use onLoad event attribute of body or jQuery's ready.

https://code.sololearn.com/WgIYruSt82PG/?ref=app