I found an answer, but it was for JQuery. Here is the link:
http://jquerybyexample.blogspot.com/2010/12/disable-cut-copy-and-paste-function-for.html
: I want something in plain Javascript which work on chrome, latest firefox, safari, and IE 8 and 9.
Update
Due to all the negative comments saying that this is a bad idea for an internet site I can only say “I agree”. Please note that this is for an “intranet” application where cut, copy, and paste need to be overidden as the default browser behaviour for cut copy and paste needs to be customized to handle embedded tags in a rich text area
of course it is not appropriate to do stuff like this, but that was not @Zubairs question, so i think voting down is not correct here, as he made his point clear.
now to the question: if jQuery can do it, native javascript can do it of course too.
you must prevent the cut, copy and paste events:
this prevents the right-click-context-menu, this is not needed if you use the 3 other event-handlers but just to let you know 😉
IMPORTANT: the body must be loaded (of course), document.body because IE needs it (document.oncopy will only work in chrome/firefox/safari)