Call server side function on Function key press

<script type="text/javascript">

document.onkeyup = KeyCheck;
function KeyCheck(e) {
    var KeyID = (window.event) ? event.keyCode : e.keyCode; switch (KeyID) {
        case 118:
            __doPostBack('__Page', 'F7');
            break;       
        case 39:
            //__doPostBack('__Page', 'ArrowRight');
            __doPostBack('Button2', '')
            break;
        case 40:
            __doPostBack('__Page', 'ArrowDown'); break;
    }
}
</script>

<form id="form1" runat="server">
     <a id="LButton3" href="javascript:__doPostBack('Button2','')">LinkButton</a>
     <a id="A1" href="DisableBackButton.aspx">LinkButton</a>
     <asp:Button ID="Button2" runat="server" onclick="Button2_Click" Text="Button" />   
</form>

Server Side Code

protected void Page_Load(object sender, EventArgs e)
    {
        Response.Write(DateTime.Now.ToString());
        Page.ClientScript.GetPostBackEventReference(this, "");
        string eventArgs = Request["__EVENTARGUMENT"]; if (!string.IsNullOrEmpty(eventArgs))
        {
            switch (eventArgs)
            {
                case "F7":
                    a("F7");
                    break; 
            }
        }
    }

public void a(string s)
    {
        Response.Write(s);
    }