Asp.net click the button to submit and the button becomes unavailable

. Aspx
Copy codeThe Code is as follows:
<Script language = "javascript">
Function abc ()
{
Var mybutton = document. getElementById ("Submit1 ");
Mybutton. disabled = true; // gray
_ DoPostBack ("Submit1", ""); // executes the click event of Submit1 on the server.
}
</Script>
<Form id = "Form1" method = "post" runat = "server">
...
<INPUT id = "Submit1" type = "submit" value = "Start upload" name = "Submit1" runat = "server">
....
</Form>

. Cs
Copy codeThe Code is as follows:
Private void Page_Load (object sender, System. EventArgs e)
{
...
This. GetPostBackEventReference (Submit1); // this sentence is critical. this sentence allows the client to execute server events.
Submit1.Attributes. Add ("onclick", "abc ();");
....
}