What potential security risks should be considered when passing variables from JavaScript to PHP?

When passing variables from JavaScript to PHP, one potential security risk to consider is the possibility of injection attacks, where malicious code is inserted into the variables. To prevent this, it is important to sanitize and validate the input data before using it in PHP code. This can be done by using functions like htmlspecialchars() to escape special characters and prevent script injection.

// Sanitize and validate input data from JavaScript
$variable = htmlspecialchars($_POST['variable']);