How do i get just 1 element JS

i am trying to add hcaptcha to my website but i am doing it in a strange way i want to get if the div with the class ‘check’ is hidden or not but i cannot do it.
here is my code

    var x = document.getElementsByClassName("check")[0]
    var y = window.getComputedStyle(x).display
    alert(y)

it gives me the error ‘cip.html:62 Uncaught TypeError: Failed to execute ‘getComputedStyle’ on ‘Window’: parameter 1 is not of type ‘Element’.
at cip.html:62′

>Solution :

You need to verify that x is not undefined in case none of the elements have the class your looking for

var x = document.getElementsByClassName("check")[0]
if (x) {
  var y = window.getComputedStyle(x).display
  alert(y)
} else {
  alert('not found')
}