How can i do this in JavaScript?

When you copy data from this website it include some source code which backlink to that page, how i can do the same in JS.

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I can't give you the javascript because that would mean to violate

http://www.tynt.com

Code (markup):

rights.
So if you want to use it too go to

http://www.tynt.com/

Code (markup):

! Cheers.

 

I've seen those to, if you find a script please share. There must be some freeones out there.