title: How to stop form submit during ajax call
body: <p>I can only modify the code in the ajax call.
  The ajax call occurs when I click the submit in form named <code>$('#form1')</code>.</p>
  
  <pre><code>$('#form1').submit(function () {
      $.ajax({
         url: 'some.php',
         type: 'POST',
         data: somedata,
         success: function (msg) {
            if (!msg) {
               // I wanna to stop '#form1' submit here,how to do that? I can only modify the code in the ajax call.
            }
         }
      });
   });
  </code></pre>