<input type="email" id="testEmail" >

<div id="results"></div>

#testEmail {
  display: none;
}

let result = document.querySelector("#results");
function divLog(s) {
  result.innerHTML += s + '<br/>';
}

let emailField = document.querySelector("#testEmail");
let tests = [
  "foo@foo.com",
  "foo",
  "goo@goo.com",
  "zoo"
];

tests.forEach(t => {
  emailField.value = t;
  divLog(`Is ${t} a valid email? ${emailField.checkValidity()}`);
});