Cannot read property (name of it) of null

Question

Please someone tells me why i get this kind of error

Answer 1

Use
window.onload=function(){
Correct js code
}

Answer 2

Try this

window.onload = () => {
// JS code
}

Answer 3

try with this
put your js code of js section as

document.onload = ()=>{

// put your js code here

}