How to pass variable from jquery to code behind (C#)?

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 f function in onClientClick and if the element has id you can just use the id to select it with #

<head id="Head1" runat="server">
<title>Pass Javascript Variables to Server</title>
     <script type="text/javascript">             // Second Step
         function f() {
             $("input[id*='inpHide']").val("My JavaScript Value");
         }
    </script>
</head>

<body>
    <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>

Your <input> tag needs a name attribute, or it won't be posted.

The response from Sean McMillan is right, but I think you also need to change this :

<asp:Button ID="btnJSValue" Text="Click" runat="server" OnClientClick="f"/>

<asp:Button ID="btnJSValue" Text="Click" runat="server" OnClientClick="f();"/>

来源：https://stackoverflow.com/questions/6997810/how-to-pass-variable-from-jquery-to-code-behind-c

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