title: how to use beforeSend option in $.post()
body: <p>I'm using ajax and I use beforeSend option in It .. But I want to know how to use 
  beforeSend option  in $.post() ...</p>
  
  <p>my ajax code : </p>
  
  <pre><code>$.ajax({
      type: 'POST',
      url: url,
      data: data,
      beforeSend: function () {
          //some condition 
      },
      success: function (){},
      error: function () {}
  });
  </code></pre>
  
  <p>In $.post() :</p>
  
  <pre><code>$.post(url, data, function())
  </code></pre>
  
  <p>But when to add beforeSend option</p>