How to manipulate the __doPostBack JavaScript function

F=Greetings all

I am trying to manipulate the JavaScript PostBack, in order to set a field value. My problem lies in the __doPostback call, in the JavaScript, as when I remove that line, things run as supposed to.

Suggestions?


In advance, thanks!

<SCRIPT LANGUAGE="JavaScript">    
function DoPostBack()
{   document.getElementById("HiddenField1").value = "ABCDE"
    __doPostBack(\'ListBox1\',\'\')', 0);
   alert("Hello 1"); 
}            
  
</SCRIPT>            
 
<asp:ListBox ID="ListBox1" runat="server" AutoPostBack="True" 
    Style="z-index: 100; left: 102px; position: absolute; top: 28px">
            <asp:ListItem>aaaaa</asp:ListItem>
            <asp:ListItem>bbbb</asp:ListItem>
            <asp:ListItem>cccc</asp:ListItem>
            <asp:ListItem>dddddd</asp:ListItem>
        </asp:ListBox>
        <asp:HiddenField ID="HiddenField1" runat="server" />
 
protected void Page_Load(object sender, EventArgs e)
    {
        ListBox1.Attributes.Add("onchange", "DoPostBack();");
 
        if (!Page.IsPostBack)
            HiddenField1.Value = "";  // Clear the field.
 
        Label1.Text = HiddenField1.Value;
 
    }

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