Java script error

Question

Hi I write a code for web but when I run it ,java script make error, I speand much time for it but I can't solve it.
https://code.sololearn.com/WFFQT4qvuvJE/?ref=app

Answer 1

1. About the error "cannot add Event Listener of null"

If you are using JS Tab of code playground, you need to ensure the scripts run after loading content by :

window.onload = function() {
.... your codes....
}

https://code.sololearn.com/WriFNOoR188j/?ref=app
https://www.sololearn.com/post/90825/?ref=app
https://www.sololearn.com/Discuss/1546397/?ref=app

2. About variable naming

Use camelBack

justLikeThis

the space is taken, the first letter of each word is capitalized.

ExampleOfCamelBackVariableNaming:

https://code.sololearn.com/WuSmsEH1LaxK/?ref=app

Answer 2

Thank u ,i do but it don't solve

Answer 3

Don't solve 😢

Answer 4

The error is because DOM related functions such as getElementById() are running before the elements exist.
Best way to solve this is to use
window.onload = function(){
//Paste whole JS here
}

But there are few more things to do as there are a few typing mistakes like
Instead of _ you used - in the CSS as well as JS file
And
You have written
getElemenTsByClassName in JS file
Fix these and it's working