阅读有关特定字符串PHP和JavaScript的更多按钮问题

<?php
$string = "这是一个特定的字符串，用于示例更多按钮的功能。这段字符串可能非常长，需要通过更多按钮来展开或隐藏。";

$maxLength = 50; // 设定初始显示长度

if (strlen($string) > $maxLength) {
    $shortString = substr($string, 0, $maxLength);
    $longString = substr($string, $maxLength);
    echo '<div id="content">' . $shortString . '<span id="more">' . $longString . '</span></div>';
    echo '<button onclick="toggleContent()">更多</button>';
} else {
    echo $string;
}
?>

<script>
function toggleContent() {
    var content = document.getElementById("content");
    var moreText = document.getElementById("more");
    var btn = document.getElementsByTagName("button")[0];

    if (moreText.style.display === "none") {
        moreText.style.display = "inline";
        btn.innerHTML = "更多";
    } else {
        moreText.style.display = "none";
        btn.innerHTML = "隐藏";
    }
}
</script>