title: change textbox value in client side and read it in server side
body: <p>I have some textbox and I change the value of this textboxes in clientside (javascript) ,value was changed but when I read in server side after postback actually value not changed. my textbox isn't read only or disable.
  notice that I use updatepanel and my postbacks is async.any idea to solve this issue?</p>
  
  <p><strong>update</strong>
  I use <a href="https://github.com/mathiasbynens/jquery-placeholder/blob/master/jquery.placeholder.js" rel="nofollow">this</a> jquery to support placeholder in ie,but it cause value of my textboxes equal to placeholder value, and this conflict when my postback is async. for solving this problem I use below jquery code:</p>
  
  <pre><code>function EndRequestPostBackForUpdateControls() {
  //*****************************For place holder support in ie******************************
  if (runPlaceHolder != 0) {
      //alert('end');
      $('input, textarea').placeholder();
  
  
      var $inputs = $('.placeholder');
      $inputs.each(function () {
  
          var $replacement;
          var input = this;
          var $input = $(input);
          var id = this.id;
          if (input.value == '') {
              if (input.type == 'password') {
                  if (!$input.data('placeholder-textinput')) {
                      try {
                          $replacement = $input.clone().attr({ 'type': 'text' });
                      } catch (e) {
                          $replacement = $('&lt;input&gt;').attr($.extend(args(this), { 'type': 'text' }));
                      }
                      $replacement
                      .removeAttr('name')
                      .data({
                          'placeholder-password': $input,
                          'placeholder-id': id
                      })
                      .bind('focus.placeholder', clearPlaceholder);
                      $input
                      .data({
                          'placeholder-textinput': $replacement,
                          'placeholder-id': id
                      })
                      .before($replacement);
                  }
                  $input = $input.removeAttr('id').hide().prev().attr('id', id).show();
                  // Note: `$input[0] != input` now!
              }
              $input.addClass('placeholder');
              $input[0].value = $input.attr('placeholder');
          } else {
              $input.removeClass('placeholder');
          }
      });
  }}
  function safeActiveElement() {
  // Avoid IE9 `document.activeElement` of death
  // https://github.com/mathiasbynens/jquery-placeholder/pull/99
  try {
      return document.activeElement;
  } catch (err) { }}
  
  function BeginRequestPostBackForUpdateControls() {
  //*****************************For place holder support in ie******************************
  if (runPlaceHolder != 0) {
      // Clear the placeholder values so they don't get submitted
      var $inputs = $('.placeholder').each(function () {
          var input = this;
          var $input = $(input);
          if (input.value == $input.attr('placeholder') &amp;&amp; $input.hasClass('placeholder')) {
              if ($input.data('placeholder-password')) {
  
                  $input = $input.hide().next().show().attr('id', $input.removeAttr('id').data('placeholder-id'));
                  // If `clearPlaceholder` was called from `$.valHooks.input.set`
                  if (event === true) {
                      return $input[0].value = value;
                  }
                  $input.focus();
              } else {
                  alert($(this)[0].value);
                  $(this)[0].value = '';
                  alert($(this)[0].value);
                  $input.removeClass('placeholder');
                  input == safeActiveElement() &amp;&amp; input.select();
              }
          }
      });
  }}
  
  $(document).ready(function () {
  
      var prm = Sys.WebForms.PageRequestManager.getInstance();
      prm.add_beginRequest(BeginRequestPostBackForUpdateControls);
  
      prm.add_endRequest(EndRequestPostBackForUpdateControls);
  
  });
  </code></pre>
  
  <p>I use this code to clear my textbox value before sending to server in add_beginRequest,and set value in add_endRequest (for placeholder in ie).
  can anyone help solve this problem? thank you.</p>