What are the best practices for integrating client-side scripting languages like JavaScript with PHP?

When integrating client-side scripting languages like JavaScript with PHP, it is important to understand the difference between server-side and client-side execution. PHP is a server-side language that generates HTML to be sent to the client, while JavaScript is a client-side language that runs in the user's browser. To integrate the two, you can use PHP to generate JavaScript code dynamically based on server-side data or user input.

<?php
// PHP code to generate JavaScript dynamically
$data = "Hello, World!";
echo "<script>";
echo "var message = '" . $data . "';";
echo "console.log(message);";
echo "</script>";
?>