title: Check if asp.net control exists with jQuery
body: <p>When referring asp.net control inside a MasterPage in this way:</p>
  
  <pre><code>    $(function() { 
          $('#&lt;%=txtMunicipio.ClientID%&gt;').autocomplete({
              source: function(request, response) {
                  $.ajax({
                      url: 'http://localhost/Autocomplete/WSAutocomplete.asmx/Poblacion',
                      data: 't=' + request.term,
                      type: 'POST',
                      //contentType: 'text/xml;charset=utf-8',
                      dataType: 'xml',
                      success: function(data) {
                          response(a = $.map(splitResponse(data), function(a, n) {
                              return formatCity(a, n);
                          }));
                      }
                  });
              },
              ........
  </code></pre>
  
  <p>I am getting error "Object expected" because control does not exist in page. How can I check if control exists before associate autocomplete function?</p>
  
  <p>Thanks in advance</p>