只需将你想要在页面加载时调用的模态包装在文档头部的jQuery load事件中，它就会弹出，如下所示:

JS

<script type="text/javascript">
    $(window).on('load', function() {
        $('#myModal').modal('show');
    });
</script>

HTML

<div class="modal hide fade" id="myModal">
    <div class="modal-header">
        <a class="close" data-dismiss="modal">×</a>
        <h3>Modal header</h3>
    </div>
    <div class="modal-body">
        <p>One fine body…</p>
    </div>
    <div class="modal-footer">
        <a href="#" class="btn">Close</a>
        <a href="#" class="btn btn-primary">Save changes</a>
    </div>
</div>

你仍然可以在你的页面中调用模态，通过这样的链接调用它:

<a class="btn" data-toggle="modal" href="#myModal">Launch Modal</a>

更新2021

引导5

现在Bootstrap不再需要jQuery，使用JavaScript显示模态很容易。

var myModal = new bootstrap.Modal(document.getElementById('myModal'), {})
myModal.toggle()

Demo

引导4

Bootstrap 4的模式标记略有变化。下面是如何在页面加载时打开模态，并可选地延迟显示模态…

$(window).on('load',function(){
    var delayMs = 1500; // delay in milliseconds
    
    setTimeout(function(){
        $('#myModal').modal('show');
    }, delayMs);
});    

<div class="modal fade" id="myModal">
      <div class="modal-dialog modal-lg modal-dialog-centered" role="document">
            <div class="modal-content">
                <div class="modal-header">
                    <h4 class="modal-title">My Modal</h4>
                    <button type="button" class="close" data-dismiss="modal" aria-label="Close">
                        <span aria-hidden="true">×</span>
                    </button>
                </div>
                <div class="modal-body">
                    ...
                </div>
                <div class="modal-footer">
                    <button type="button" class="btn btn-secondary mx-auto" data-dismiss="modal">Close</button>
                </div>
            </div>
      </div>
</div>

Demo

使用Bootstrap 3和jQuery(2.2和2.3)进行测试

$(window).on('load',function(){
  $('#myModal').modal('show');
});



<!-- Modal -->
<div class="modal fade" id="myModal" role="dialog">
    <div class="modal-dialog">

      <!-- Modal content-->
      <div class="modal-content">
        <div class="modal-header">
          <button type="button" class="close" data-dismiss="modal">&times;</button>
          <h4 class="modal-title"><i class="fa fa-exclamation-circle"></i>&nbsp; //Your modal Title</h4>
        </div>
        <div class="modal-body">
          //Your modal Content
        </div>
        <div class="modal-footer">
          <button type="button" class="btn btn-default" data-dismiss="modal">Fechar</button>
        </div>
      </div>

    </div>
</div>

https://jsfiddle.net/d7utnsbm/

在bootstrap 3中，你只需要通过js初始化模态，如果在页面加载的时刻，模态标记在页面中，模态就会显示出来。

如果你想防止这种情况，可以在初始化模态的地方使用show: false选项。就像这样: $ (' .modal ')。Modal ({show: false})

你可以使用jQuery来处理这个问题

首先在模板上导入

<script src="https://code.jquery.com/jquery-3.6.0.min.js" integrity="sha256-/xUj+3OJU5yExlq6GSYGSHk7tPXikynS7ogEvDej/m4=" crossorigin="anonymous"></script>

然后用jQuery脚本在你的模式上点击id

<script type="text/javascript">
      $(window).on('load', function() {
        $('#staticBackdrop').modal('show');
    });
</script>

这里是modal用于case显示的django消息

{% if messages %}
      {% for message in messages %}
      <div class="modal fade" id="staticBackdrop" data-bs-backdrop="static" data-bs-keyboard="false" tabindex="-1" aria-labelledby="staticBackdropLabel" aria-hidden="false">
        <div class="modal-dialog">
          <div class="modal-content">
            <div class="modal-header">
              <h5 class="modal-title" id="staticBackdropLabel">Message</h5>
              <button type="button" class="btn-close" data-bs-dismiss="modal" aria-label="Close"></button>
            </div>
            <div class="modal-body">
              {{ message }}
            </div>
            <div class="modal-footer">
              <button type="button" class="btn btn-secondary" data-bs-dismiss="modal">Close</button>
            </div>
          </div>
        </div>
      </div>
      {% endfor %}
        
    {% endif %}

为了避免引导被否决并失去它的功能，只需创建一个常规的启动按钮，为它提供一个Id，然后使用jquery“点击它”，如下所示: 启动按钮:

<button type="button" id="btnAnouncement" class="btn btn-primary" data-toggle="modal" data-target="#modalAnouncement">
  See what´s new!
</button>

jQuery触发器:

$(document).ready(function () {
  $('#btnAnouncement').click();
)}

希望能有所帮助。干杯!