Making button accept text input Javascript

Let's look at it line, by line, assuming your code is now the same as what's on CodePen.

var number = Math.floor(Math.random() * 10) + 1;
var button = document.getElementById('checkNumber');

button.addEventListener('click', function(){
  var inputNumber = document.getElementById('number');
  if (inputNumber.value == number) {
    inputNumber.value = 'Yay! ' + number + ' is correct!';
    number = Math.floor(Math.random() * 10) + 1;
  } else {
    inputNumber.value = '';
  }

});

We've got 2 variables here, one that stores a random number between 1 and 10. Since by flooring (Math.floor()) the number (rounding it down) it's actually only 1-9 so we add another number to the expression.

var button is simply letting the browser know we want to do something with the button and making sure we do something with the correct button and we do that with given id of the button element.

So next we reference the getElementById and assign it to anonymous function which wants a click action.

Inside it as where the action happens. We want to compare the users's input with the result of the random number between one and ten. If we get it right, you get the congratulatory message. If not, what the code does is provide an empty sting that clears out the input form so you can try again.

At the heart of it all is a condition statement. The expression is comparing the number given, that you provided and comparing that to the value that Math.random() generates.

I hope this makes sense to you. :-)