.innerHTML is null

Question

What does this means and how do I stop it from happening. Any additional information would extremely helpful.
Thank you for any responses that you have giving me

Answer 1

Any javascript code written inside the script tags (present in head section of your HTML file) gets executed by the browser rendering engine even before your whole DOM is loaded.
https://stackoverflow.com/questions/18239430/cannot-set-property-innerhtml-of-null
https://stackoverflow.com/questions/23136759/uncaught-typeerror-cannot-set-property-innerhtml-of-null