What are the potential pitfalls of mixing client-side JavaScript and server-side PHP code for form submission handling?

One potential pitfall of mixing client-side JavaScript and server-side PHP code for form submission handling is the risk of insecure data being sent to the server if the client-side validation is bypassed. To mitigate this risk, it's important to always validate data on the server side as well, regardless of any client-side validation that may have been implemented. 

// Server-side PHP code snippet for form submission handling with validation

if ($_SERVER["REQUEST_METHOD"] == "POST") {
    // Validate form data on the server side
    $name = htmlspecialchars($_POST["name"]);
    $email = filter_var($_POST["email"], FILTER_VALIDATE_EMAIL);
    
    // Process form data if validation passes
    if (!empty($name) && $email) {
        // Handle form submission
    } else {
        // Handle validation errors
    }
}

Keywords

JavaScript PHP form submission security vulnerabilities cross-site scripting

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