动态替换 href

您可以将链接存储在变量中。然后，单击该按钮时，检查字段是否为空（并应用任何验证规则）。如果不为空，请将提交应用于表单。

$link = 'example.com/download.pdf';
$('.button').click(function(){
    // CHECK THE FIELDS ARE NOT EMPTY
    // APPLY YOUR OWN VALIDATION
    if($field1 = $('.field1').val() != '' && $('.field2').val() != ''){
       // DO WHAT YOU NEED TO DO WITH THE LINK
       $('form').submit();
    } 
})

附带说明一下，您可能因为没有向我们提供解决自己问题的尝试而被投了反对票（不是我自己）。您向我们提供了您的 html，但没有提供任何经过测试的逻辑。

你在 JavaScript 中向按钮添加一个点击处理程序：

var fieldsAreReadyToBeSent = function() {
    // Validation code goes here
    // return true if valid & false if invalid
};
document.querySelector("[type=submit]").addEventListener("click", function() {
    if(!fieldsAreReadyToBeSent()) {
        event.preventDefault();
    }
});

该方法event.preventDefault()防止您的表单被提交，如果它被认为是无效的！

演示 ：

var fieldsAreReadyToBeSent = function() {
    return false; // FOR THIS DEMO, ALWAYS RETURN FALSE
};
document.querySelector("[type=submit]").addEventListener("click", function() {
    if(!fieldsAreReadyToBeSent()) { // FOR THIS DEMO, THIS IS ALWAYS TRUE
        event.preventDefault();
    }
});

 <div class="container">
<!-- Trigger the modal with a button -->
<a href="#example1" class="btn btn-warning btn-lg" data-toggle="modal" data-target="#myModal">Download Item #1</a>
<a href="#example2" class="btn btn-info btn-lg" data-toggle="modal" data-target="#myModal">Download Item #2</a>
<!-- 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">Modal Header</h4>
      </div>
      <div class="modal-body">
        <form role="form">
          <div class="form-group">
            <label for="email">Email address:</label>
            <input type="email" class="form-control" id="email">
          </div>
          <div class="form-group">
            <label for="pwd">Password:</label>
            <input type="password" class="form-control" id="pwd">
          </div>
          <div class="checkbox">
            <label>
              <input type="checkbox"> Remember me</label>
          </div>
          <button type="submit" class="btn btn-default">Submit</button>
        </form>
      </div>
      <div class="modal-footer">
        <button type="button" class="btn btn-default" data-dismiss="modal">Close</button>
      </div>
    </div>
  </div>
</div>
  </div>