This works well for me:
jQuery(document).ready(function($) {
var intputElements = document.getElementsByTagName("INPUT");
for (var i = 0; i < intputElements.length; i++) {
intputElements[i].oninvalid = function (e) {
e.target.setCustomValidity("");
if (!e.target.validity.valid) {
if (e.target.name == "email") {
e.target.setCustomValidity("Please enter a valid email address.");
} else {
e.target.setCustomValidity("Please enter a password.");
}
}
}
}
});
and the form I'm using it with (truncated):
<form id="welcome-popup-form" action="authentication" method="POST">
<input type="hidden" name="signup" value="1">
<input type="email" name="email" id="welcome-email" placeholder="Email" required></div>
<input type="password" name="passwd" id="welcome-passwd" placeholder="Password" required>
<input type="submit" id="submitSignup" name="signup" value="SUBMIT" />
</form>