Javascript focus and functions with textBox

Set Focus function on server side code (just pass in the string of the control name)

protected void setFocus( String ctrl )
{
string s = "[SCRIPT language='javascript']document.Form1.Editor1_" + ctrl + ".focus();[/SCRIPT]";
Page.RegisterStartupScript( "focus", s );
}

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Function on server side code to assign javascript event to a particular ASP.NET control (Change the details passed to JavaScript function for each call)

txtStartDateDay.Attributes.Add("onkeyup", "SetFocusX('Editor1_txtStartDateDay','Editor1_txtStartDateMonth')");

In the HTML JavaScript function (checks the lenght of the field if two sets focus to the next)

function SetFocusX(oField, oField2)
{
var strText = document.getElementById(oField).value;
if(strText.length == 2)
{
document.getElementById(oField2).focus();
}
}