Assign value to TextBox using jQuery in ASP.Net

hello,

i have this javascript function i am not sure why this is not working

function cl() {
    var textbox1 = $(this).find('[id*=TextBox1]').val();
    textbox1.val = "Chnaged";
    document.getElementById("<%=Button1.ClientID %>").click();
}

<asp:TextBox ID="TextBox1" runat="server"></asp:TextBox>
<asp:Button ID="Button2" Text="Upload" runat="server" OnClientClick="cl()" />
<asp:Button ID="Button1" runat="server" Text="Button" OnClick="Button1_Click" />
<asp:Label ID="Label1" runat="server" Text="firstvalue"></asp:Label>