How to copy text to the clipboard?

Thanks got this Zsolt - just built an troubleshooter that sits in an iframe pop-up within one of our tools, and this JS copies some text across to an email which can then be sent straight to our IT dept when things go wrong. Super useful!

Last piece of the jigsaw. When the text is copied, in the top left of the browser it shows a text box with the copied text. I believe this is because the JS creates the textboc then copies its contents. So how can I get the textbox to delete after this has taken place?

Thanks for any help!