Onclick not added until after Postback

Question

I have the following:

<asp:Button id="SubmitButton" Text="Submit" runat="server" OnClientClick="Do();"  
     OnClick="SubmitButton_Click"/>

When the page is first rendered, I go to the view source in my browser and see that the onclick="Do();" is not added to my submit button tag. But when I do a post back, and do the view source again, the onclick is added to the submit.

Why would the onclick not be there on the first request?

Answer 1

At least on my machine, I can see OnClick event on both request.