Please, what is wrong with my java code?

Question

I keep getting an uncaught error on line 2 and I don't know how to fix it.
https://code.sololearn.com/WrWmrhTLZua7/?ref=app
https://code.sololearn.com/WrWmrhTLZua7/?ref=app
https://code.sololearn.com/WrWmrhTLZua7/?ref=app

Answer 1

onload=()=>{
var button = document.querySelector("#button");
button.onclick = function() {
alert("Welcome");
}};

//it's javascript code, not java