如何在socketio返回中传递PHP函数/变量

<?php
$message = "Hello from PHP!";
function calculateSum($a, $b) {
    return $a + $b;
}
?>

<?php
// 引入socket.io客户端库
echo '<script src="https://cdn.socket.io/4.3.1/socket.io.min.js"></script>';

// 将函数和变量传递给前端
echo '<script>';
echo 'var socket = io();';
echo 'socket.emit("phpData", {';
echo '    message: "' . $message . '",';
echo '    sum: ' . calculateSum(2, 3) . '';
echo '});';
echo '</script>';
?>

<script>
var socket = io();

socket.on('phpData', function(data) {
    var message = data.message;
    var sum = data.sum;

    console.log(message); // 输出：Hello from PHP!
    console.log(sum); // 输出：5
});
</script>