Automatically Scrolling Down The Page To The Bottom After Adding Data To It By Xmlhttpreq Object?

I use xmlhttpreq object to add data to the current html file.
It will add to a specifiy place, like after a tag or before a tag
And if it adds too many data after that tag, the whole page will become
big and need to scroll down to see the latest added data
how to let it scroll down automatically without any annoying scrolling
down?

One way I can use is to use a anchor which is at the bottom of that
page and after i put my data into the textbox and click the link( which
is linked to proper file to process the data but also point to the
anchor) the page will show from the bottom. but the whole page will
first jump up a little space then jump down.