Access content page control from master page using javascrip

Question

Hey Friend,

      I want to access content page control from master page object using javascript function.but it is not working , any help with the same.

using this code:

 

 

 

  <script type="text/javascript">

function GoToNextTab() {

var txtCont = document.getElementById("Page.Master.FindControl('ContentPlaceHolder1').FindControl('Tab2')").value;

txtCont.Attributes["class"]="selected";

}

 </script>

 

 

 call a function from html button:

<button class="btn btn-success nextBtn btn-lg pull-right" type="button" onclick="GoToNextTab()" tabindex="38">??? ????..</button>