接收到来自ajax的结果后，打开一个弹出框

您可以

$("#bsModal3").modal('show');

进一步了解模态方法

$.ajax({  type: 'post',  url: 'test2.php',  dataType: 'json',  data: {    txt: txtbox,    hidden: hiddenTxt  },  cache: false,  success: function(returndata) {    if (returndata[4] === 1) {      $("#bsModal3").modal('show');    } else {      // other pre    }  },  error: function() {    console.error('Failed to process ajax !');  }});<link href="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.5/css/bootstrap.min.css" rel="stylesheet" /><script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script><script src="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.5/js/bootstrap.min.js"></script><!-- Modal --><div  id="bsModal3" tabindex="-1" role="dialog" aria-labelledby="mySmallModalLabel" aria-hidden="true">  <div >    <div >      <div >        <button type="button"  data-dismiss="modal" aria-hidden="true">&times;</button>        <h4  id="mySmallModalLabel">Modal title</h4>      </div>      <div >        Your content goes here...      </div>      <div >        <button type="button"  data-dismiss="modal">Close</button>        <button type="button" >Save changes</button>      </div>    </div>  </div></div>