Javascript 引导模式未在PHP中显示

我正在创建一个基于PHP的登录页面，我试图确保如果出现服务器错误，将显示一个模式。但当我尝试这样做时，控制台中会显示一个错误

未定义“$”

如何制作情态剧

我试图检查代码是否实际运行，并且它正在运行

文件中的模式：

<div class="modal fade bd-example-modal-xl" id="server-error" tabindex="-1" role="dialog" aria-labelledby="server-error" aria-hidden="true">
    <div class="modal-dialog modal-xl" role="document">
        <div class="modal-content">
            <div class="modal-header">
                <h5 class="modal-title" id="exampleModalLabel">Server error</h5>
                <button type="button" class="close" data-dismiss="modal" aria-label="Close">
                    <span aria-hidden="true">&times;</span>
                </button>
            </div>
            <div class="modal-body">
                Server error, Please contact AlexDorian7.
            </div>
            <div class="modal-footer">
                <button type="button" class="btn btn-secondary" data-dismiss="modal">Close</button>
            </div>
        </div>
    </div>
</div>

---

谢谢

检查您是否拥有与引导相关的所有脚本和css

<script src="https://ajax.googleapis.com/ajax/libs/jquery/3.4.1/jquery.min.js"></script>
<link href="https://stackpath.bootstrapcdn.com/bootstrap/4.3.1/css/bootstrap.min.css" rel="stylesheet">
<script src="https://stackpath.bootstrapcdn.com/bootstrap/4.3.1/js/bootstrap.min.js"></script>


<script type="text/javascript">
    function showServerErrorMessage() {
        $("#server-error").modal('show');
    }
</script>

函数showServerErrorMessage（）{
$（“#服务器错误”）.modal（'show'）；
}

在上面定义函数后调用该函数

<?php if ($conn->connect_error) { ?>
<script type="text/javascript"> showServerErrorMessage(); </script>
<?php } ?>

<div class="modal fade bd-example-modal-xl" id="server-error" tabindex="-1" role="dialog" aria-labelledby="server-error" aria-hidden="true">
    <div class="modal-dialog modal-xl" role="document">
        <div class="modal-content">
            <div class="modal-header">
                <h5 class="modal-title" id="exampleModalLabel">Server error</h5>
                <button type="button" class="close" data-dismiss="modal" aria-label="Close">
                    <span aria-hidden="true">&times;</span>
                </button>
            </div>
            <div class="modal-body">
                Server error, Please contact AlexDorian7.
            </div>
            <div class="modal-footer">
                <button type="button" class="btn btn-secondary" data-dismiss="modal">Close</button>
            </div>
        </div>
    </div>
</div>

showServerErrorMessage（）；

您可以将模型放在页面的任何位置

<?php if ($conn->connect_error) { ?>
<script type="text/javascript"> showServerErrorMessage(); </script>
<?php } ?>

<div class="modal fade bd-example-modal-xl" id="server-error" tabindex="-1" role="dialog" aria-labelledby="server-error" aria-hidden="true">
    <div class="modal-dialog modal-xl" role="document">
        <div class="modal-content">
            <div class="modal-header">
                <h5 class="modal-title" id="exampleModalLabel">Server error</h5>
                <button type="button" class="close" data-dismiss="modal" aria-label="Close">
                    <span aria-hidden="true">&times;</span>
                </button>
            </div>
            <div class="modal-body">
                Server error, Please contact AlexDorian7.
            </div>
            <div class="modal-footer">
                <button type="button" class="btn btn-secondary" data-dismiss="modal">Close</button>
            </div>
        </div>
    </div>
</div>

服务器错误
&时代；
服务器错误，请联系AlexDorian7。
接近

请检查您是否拥有与引导相关的所有脚本和css

<script src="https://ajax.googleapis.com/ajax/libs/jquery/3.4.1/jquery.min.js"></script>
<link href="https://stackpath.bootstrapcdn.com/bootstrap/4.3.1/css/bootstrap.min.css" rel="stylesheet">
<script src="https://stackpath.bootstrapcdn.com/bootstrap/4.3.1/js/bootstrap.min.js"></script>


<script type="text/javascript">
    function showServerErrorMessage() {
        $("#server-error").modal('show');
    }
</script>

函数showServerErrorMessage（）{
$（“#服务器错误”）.modal（'show'）；
}

在上面定义函数后调用该函数

<?php if ($conn->connect_error) { ?>
<script type="text/javascript"> showServerErrorMessage(); </script>
<?php } ?>

<div class="modal fade bd-example-modal-xl" id="server-error" tabindex="-1" role="dialog" aria-labelledby="server-error" aria-hidden="true">
    <div class="modal-dialog modal-xl" role="document">
        <div class="modal-content">
            <div class="modal-header">
                <h5 class="modal-title" id="exampleModalLabel">Server error</h5>
                <button type="button" class="close" data-dismiss="modal" aria-label="Close">
                    <span aria-hidden="true">&times;</span>
                </button>
            </div>
            <div class="modal-body">
                Server error, Please contact AlexDorian7.
            </div>
            <div class="modal-footer">
                <button type="button" class="btn btn-secondary" data-dismiss="modal">Close</button>
            </div>
        </div>
    </div>
</div>

showServerErrorMessage（）；

您可以将模型放在页面的任何位置

<?php if ($conn->connect_error) { ?>
<script type="text/javascript"> showServerErrorMessage(); </script>
<?php } ?>

<div class="modal fade bd-example-modal-xl" id="server-error" tabindex="-1" role="dialog" aria-labelledby="server-error" aria-hidden="true">
    <div class="modal-dialog modal-xl" role="document">
        <div class="modal-content">
            <div class="modal-header">
                <h5 class="modal-title" id="exampleModalLabel">Server error</h5>
                <button type="button" class="close" data-dismiss="modal" aria-label="Close">
                    <span aria-hidden="true">&times;</span>
                </button>
            </div>
            <div class="modal-body">
                Server error, Please contact AlexDorian7.
            </div>
            <div class="modal-footer">
                <button type="button" class="btn btn-secondary" data-dismiss="modal">Close</button>
            </div>
        </div>
    </div>
</div>

服务器错误
&时代；
服务器错误，请联系AlexDorian7。
接近

“$”未定义”表示在jquery不可用/找不到时尝试使用jquery函数（本例中为选择器）。“$”未定义”表示在jquery不可用/找不到时尝试使用jquery函数（本例中为选择器）。是！非常感谢。我更改了代码，使其没有回声，而jquery链接位于代码下方，我将其向上移动。谢谢你的回答！对非常感谢。我更改了代码，使其没有回声，而jquery链接位于代码下方，我将其向上移动。谢谢你的回答！