Source Code: (back to article)
<form id="loginForm">
Username: <input type="text" name="username" required>
Password: <input type="password" name="password" required>
<button type="submit">Login</button>
</form>

<script>
document.getElementById('loginForm').addEventListener('submit', function(event) {
event.preventDefault(); // Prevent the form from submitting normally
if (this.username.value.length < 4 || this.password.value.length < 4) {
alert('Username and password must be at least 4 characters long.');
} else {
this.submit(); // Submit the form manually if validation passes
alert('successfully submitted');
}
});
</script>