A Code From A Video Course

Question

Could anyone advise me why this code that I just copied word for word from a course does not work?
https://code.sololearn.com/WWz1w43BWge6/?ref=app

Answer 1

https://code.sololearn.com/WWz1w43BWge6/?ref=app#html
// See the code

Answer 2

// First the application Sololearn have any problem, he is load the Script before code HTML Body

// Second, you forgot about single quotes at the beginning of these DOM searches.
document.getElementById(number1').innerHTML ="";
document.getElementById(number2').innerHTML ="";

// Third, you wrote the wrong property, the correct one was "Check", exactly as found in DOM
var btn = document.querySelector('input[type=button][value=check]');