Not working Tab key in login form

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ASP.NET

Javascript

jQuery

keycode

Dear All,
I have login form for authenticate user, I am using script to focus to password textbox when use press key on username textbox.

function Focus(e) {
           
            alert(e.keyCode);}
<asp:TextBox ID="txtUsername" runat="server" TabIndex="0" onkeypress="return Focus(window.event);"></asp:TextBox>

Alert is working all keycode but when I press spacial key like tab, Enter,Backspace etc then it is not working.

I need to get the keycode of Tab key of keyboard so I am able to focus on password textbox when user press tab key on username textbox.

Thank you very much in advance!