C# ImageButton Add Attributes on OnClick Event not working

Hi, 


I have two ImageButtons, and on the event OnClick of one of them, I want to aadd attributes to execute javascript onclick.
So, the ImageButton method goes something like this:
protected void imgBtnForward_Click(object sender, EventArgs e)
    {
        imgBtnForward.Attributes.Add("onclick", "javascript:alert('aaa');");
        imgBtnBack.Attributes.Add("onclick", "javascript:alert('aaa');");
    }



imgBtnForward is the sender one. After executing this, the alert added to the imgBtnBack works fine, however, the alert added to the ...