What it does mean by ! in this function?

Question

function myFunction() {
var inpObj = document.getElementById("id1");
if (!inpObj.checkValidity()) {
document.getElementById("demo").innerHTML = inpObj.validationMessage;
}
}

Answer 1

! is the not-operator
Meaning, that true becomes false and vice versa.

So in this example the validation message will be shown, if the object is not valid.
At least I assume so, I don't know much about JavaScript.

But ! is definitley the not-operator.
!true = false
!false = true