What potential pitfalls can arise when passing PHP variables to JavaScript, especially when using JSON_ENCODE?

When passing PHP variables to JavaScript using JSON_ENCODE, potential pitfalls can arise if the PHP variables contain special characters that can break the JavaScript code. To avoid this issue, it is important to properly escape the PHP variables before encoding them to JSON. This can be done using the PHP function json_encode() in combination with the JSON_HEX_TAG option, which will escape "<", ">", "&", "'", and """ characters.

$phpVariable = 'This is a <script>alert("danger!")</script>';
$escapedVariable = json_encode($phpVariable, JSON_HEX_TAG);
echo "<script>var jsVariable = {$escapedVariable};</script>";