keypress event not fired for pressing TAB or ENTER or BACK

<asp:TextBox ID="txtUser" runat="server" Font-Size="Small"  AutoPostBack="true" 
     TabIndex="2" Width="150px" 
     onkeypress="getFocus(event);" ></asp:TextBox>
...
function getFocus(event) {
   var chCode = ('charCode' in event) ? event.charCode : event.keyCode;
   //if (chcode == 9 || chcode = 13) {  // Tab or Enter
   //    document.getElementById("txtPassword").focus();
   //}
}