cannot read appenChild property

Question

why in sololearn i can't get the javascript appendChild to works in my code?
while the same codes works in my desktop visual studio code and codepen.io

here at sololearn:

https://code.sololearn.com/Wq2VQ424OurJ/?ref=app

i commented out the manual div for chessgrid

and here is my codepen:

https://codepen.io/sobadrdb/pen/KKVJBBX

they are both same javascript code.

thanks

Answer 1

Put the whole thing inside onload function:
window.onload = function(){
// your code here
}