Not able to get value of html textboxes in javascript

[justfoad]

Guys I have a issue in my code that I want to get value of html input type textboxes in javascript and assign value to hidden field.After that I want to used hidden field value in code behind file in c#, But hidden field always contains empty string Even if inputtype text boxes contain value.My Java script:\[code\] <script type ="text/javascript" > function myFunction() { var str1 = document.getElementById("amt3").value; var str2 = document.getElementById("amt4").value; document.getElementById("hf1").value = http://stackoverflow.com/questions/15698582/str1; document.getElementById("hf2").value = http://stackoverflow.com/questions/15698582/str2; } </script>\[/code\]My HTML:\[code\]<div class="form-row row-fluid"> <div class="span12"> <div class="row-fluid"> <label class="form-label span4" for="slider"> Range slider</label> <div class="span8"> <asp:UpdatePanel ID="UpdatePanel2" runat="server"> <ContentTemplate > <asp:HiddenField ID="hf1" runat="server" /> <asp:HiddenField ID="hf2" runat="server" /> <div id="slider-range" class="slider" > </div> <input type="text" id="amount1" style="border: 0; color: #ED7A53; font-weight: bold; box-shadow: none;" /> <input type="text" id="amt3" value="http://stackoverflow.com/questions/15698582/10" runat="server" style="border: 0; color: #ED7A53; font-weight: bold; box-shadow: none;" /> <input type="text" id="amt4" value="http://stackoverflow.com/questions/15698582/20" runat="server" name="amt4" style="border: 0; color: #ED7A53; font-weight: bold; box-shadow: none;" /> <asp:LinkButton ID="lnk" runat="server" onclick="lnk_Click" OnClientClick ="myFunction()">LinkButton</asp:LinkButton> </ContentTemplate> </asp:UpdatePanel>\[/code\]