What are the differences between executing JavaScript (JS) on the client side and PHP on the server side in the context of form field values?

When executing JavaScript on the client side, form field values can be easily accessed and manipulated in real-time without requiring a page reload. On the other hand, when using PHP on the server side, form field values are submitted to the server for processing after the form is submitted, which may involve a page refresh. To ensure consistency between client-side and server-side values, it is important to properly validate and sanitize input data on both ends.

<?php
// Retrieve form field value submitted via POST request
$field_value = $_POST['field_name'];

// Validate and sanitize the input data
$cleaned_value = filter_var($field_value, FILTER_SANITIZE_STRING);

// Use the cleaned value for further processing
echo "Cleaned value: " . $cleaned_value;
?>