KeyUp Function not firing on textbox ASP.NET Web Form

Hi Guys,, I'm trying to make format currency in Indonesian using javascript but why the textbox not firing when keyboard pressed.if this code running in html working properly, but not in ASP.NET. Anny help could be appriciate.

Currency Format in Javascript

Code Bihind

protected void Page_Load(object sender, EventArgs e)
    {
        txtCurrency.Attributes.Add("onkeyup", "FormatRupiah(this)");
    }