Here is my code, but it doesn’t work (code behind gets empty string):
`
<head id="Head1" runat="server">
<title>Pass Javascript Variables to Server</title>
<script type="text/javascript"> // Second Step
function f() {
$("[id$='inpHide']").val("My JavaScript Value");
}
</script>
</head>
<body onload="SetHiddenVariable()">
<form id="form1" runat="server">
<div>
<input id="inpHide" type="hidden" runat="server" />
<asp:Button ID="btnJSValue" Text="Click" runat="server" OnClientClick="f"/>
<asp:Button ID="Button1" runat="server" Text="Button" onclick="Button1_Click" />
</div>
</form>
</body>
`
There were couple of issues in your code. The parenthesis were missing while calling
ffunction inonClientClickand if the element has id you can just use the id to select it with#