What are some best practices for implementing form validation in PHP, considering both client-side and server-side validation?

When implementing form validation in PHP, it is best practice to perform both client-side and server-side validation. Client-side validation can help improve user experience by providing immediate feedback, while server-side validation ensures data integrity and security. By combining both methods, you can create a robust validation system for your forms. 

// Client-side validation using JavaScript
<script>
function validateForm() {
    var x = document.forms["myForm"]["email"].value;
    if (x == "") {
        alert("Email must be filled out");
        return false;
    }
}
</script>

<form name="myForm" action="/submit_form.php" onsubmit="return validateForm()" method="post">
    Email: <input type="text" name="email">
    <input type="submit" value="Submit">
</form>

// Server-side validation in submit_form.php
<?php
$email = $_POST['email'];

// Validate email format
if (!filter_var($email, FILTER_VALIDATE_EMAIL)) {
    echo "Invalid email format";
} else {
    // Process form data
}
?>

Keywords

form validation PHP client-side validation server-side validation error handling

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