<!DOCTYPE html>
<html>
<body>
E-mail: <input type="email" id="myEmail" maxlength="30">
<p>Click the button to display the value of the maxlength attribute of the email field.</p>
<button onclick="myFunction()">Try it</button>
<p id="demo"></p>
<script>
function myFunction() {
var x = document.getElementById("myEmail").maxLength;
document.getElementById("demo").innerHTML = x;
}
</script>
</body>
</html>