JavaScript returns an error when using innerHTML

Question

Here is the code link, https://code.sololearn.com/WLAIVQWs20NM/?ref=app

Answer 1

On sololearn, the page has to load before accessing it with JavaScript. So instead of:

var elem = document.getElementById("test");

Do:

var elem;
window.onload = function() {
elem = document.getElementById("test");
}

Answer 2

Thanks, it works very okkkey