<html>
<head>
<meta charset="utf-8">
<title>Detailed custom validation</title>
<style>
body {
font: 1em sans-serif;
width: 200px;
padding: 0;
margin : 0 auto;
}
p * {
display: block;
}
input[type=email]{
-webkit-appearance: none;
appearance: none;
width: 100%;
border: 1px solid #333;
margin: 0;
font-family: inherit;
font-size: 90%;
box-sizing: border-box;
}
/* This is our style for the invalid fields */
input:invalid{
border-color: #900;
background-color: #FDD;
}
input:focus:invalid {
outline: none;
}
/* This is the style of our error messages */
.error {
width : 100%;
padding: 0;
font-size: 80%;
color: white;
background-color: #900;
border-radius: 0 0 5px 5px;
box-sizing: border-box;
}
.error.active {
padding: 0.3em;
}
</style>
</head>
<body>
<form novalidate>
<p>
<label for="mail">
<span>Please enter an email address:</span>
<input type="email" id="mail" name="mail" required minlength="8">
<span class="error" aria-live="polite"></span>
</label>
</p>
<button>Submit</button>
</form>
<script>
// There are many ways to pick a DOM node; here we get the form itself and the email
// input box, as well as the span element into which we will place the error message.
const form = document.getElementsByTagName('form')[0];
const email = document.getElementById('mail');
const emailError = document.querySelector('#mail + span.error');
email.addEventListener('input', function (event) {
// Each time the user types something, we check if the
// form fields are valid.
if (email.validity.valid) {
// In case there is an error message visible, if the field
// is valid, we remove the error message.
emailError.innerHTML = ''; // Reset the content of the message
emailError.className = 'error'; // Reset the visual state of the message
} else {
// If there is still an error, show the correct error
showError();
}
});
form.addEventListener('submit', function (event) {
// if the form contains valid data, we let it submit
if(!email.validity.valid) {
// If it isn't, we display an appropriate error message
showError();
// Then we prevent the form from being sent by canceling the event
event.preventDefault();
}
});
function showError() {
if(email.validity.valueMissing) {
// If the field is empty
// display the following error message.
emailError.textContent = 'You need to enter an e-mail address.';
} else if(email.validity.typeMismatch) {
// If the field doesn't contain an email address
// display the following error message.
emailError.textContent = 'Entered value needs to be an e-mail address.';
} else if(email.validity.tooShort) {
// If the data is too short
// display the following error message.
emailError.textContent = `Email should be at least ${ email.minLength } characters; you entered ${ email.value.length }.`;
}
// Set the styling appropriately
emailError.className = 'error active';
}
</script>
</body>
</html>
I am reading the form-validation tutorial on MDN. As far as I understand, basically it assigns"error active"(two classes on same element) classes to span element while invalid, however in the style tag, it uses ".error.active" to refer to the element. Isn't that a descendant selector which will select element with "active" class INSIDE element with "error"class? Since there is no such elements, what does that mean?
