Why i get error?

Question

https://code.sololearn.com/WcmhD8L9BObH/?ref=app

Answer 1

'Html loading after JS'
#check the answers below
https://www.sololearn.com/discuss/1339071/?ref=app

Answer 2

Its sololearn's bug?
i get this error many times too.

just input js code into <script> tag
https://www.sololearn.com/discuss/1445422/?ref=app

Answer 3

thanks Lord Krishna !

i add :
window.onload = function{
#my code
}

https://code.sololearn.com/WJ0TV6lDk3om/?ref=app