在PHP中使用HTML / Javascript中的局部变量的不同方法

<?php
$myVariable = "Hello World!";
echo '<script>var jsVariable = "' . $myVariable . '";</script>';
?>

<?php
$myVariable = "Hello World!";
?>
<script>
    var jsVariable = "<?php echo $myVariable; ?>";
</script>

<?php
$myVariable = "Hello World!";
?>
<script>
    // 使用AJAX向服务器发送请求
    var xhr = new XMLHttpRequest();
    xhr.open("GET", "get_variable.php", true);
    xhr.onreadystatechange = function() {
        if (xhr.readyState === 4 && xhr.status === 200) {
            var jsVariable = xhr.responseText;
            // 在这里使用jsVariable
        }
    };
    xhr.send();
</script>

<?php
$myVariable = "Hello World!";
echo $myVariable;
?>