当Textbox AutoPostBack为True时，首次单击时ASP.NET按钮单击不起作用

<script>
    function textChanged() {
        var btn = document.getElementById("btnSubmit");
        btn.click();
    }
</script>

<asp:TextBox ID="txtInput" runat="server" AutoPostBack="True" onchange="textChanged()"></asp:TextBox>
<asp:Button ID="btnSubmit" runat="server" Text="Submit" OnClick="btnSubmit_Click" />

<asp:UpdatePanel ID="updatePanel" runat="server">
    <ContentTemplate>
        <asp:TextBox ID="txtInput" runat="server" AutoPostBack="True"></asp:TextBox>
        <asp:Button ID="btnSubmit" runat="server" Text="Submit" OnClick="btnSubmit_Click" />
    </ContentTemplate>
</asp:UpdatePanel>

<script src="https://code.jquery.com/jquery-3.6.0.min.js"></script>
<script>
    $(document).ready(function () {
        $("#txtInput").change(function () {
            $.ajax({
                type: "POST",
                url: "YourPage.aspx/HandleTextChanged",
                data: JSON.stringify({ text: $(this).val() }),
                contentType: "application/json; charset=utf-8",
                dataType: "json",
                success: function (response) {
                    // 处理返回的结果
                }
            });
        });
    });
</script>

<asp:TextBox ID="txtInput" runat="server" AutoPostBack="False"></asp:TextBox>
<asp:Button ID="btnSubmit" runat="server" Text="Submit" OnClick="btnSubmit_Click" />