Most of people know the following codes.
btn.Attributes.Add("onclick", "return confirm('single " & strMessage & " single ');")
what I want to mention is "return confirm('" & strMessage & "')
sometime in development, you may need to do string manipulation. the similar case could be happened any time.
For reference purpose, I've hosted this post. If someone can reference on this, I am worth to put this post.