The reasoning is that automatic copying to clipboard can be very dangerous, thus most browsers (except IE)* make it difficult unless you use flash.
Much like your ZeroClipboard, there is Clipboard LMCButton which also uses a small flash script running in the background.
A common solution would be to do this:
function copyToClipboard (text) {
window.prompt ("Copy to clipboard: Ctrl+C, Enter", text);
}
Which I found from Jarek Milewski when some one else asked the question here
*Yes I found one solution for IE, however does not work in most modern browsers, check here.
Update:
According to this: https://developer.mozilla.org/en-US/docs/Web/API/Document/execCommand Firefox 41+, Chrome 42+, and IE 9+ support the copy command with execCommand. For firefox and chrome it will only work if triggered by a user action such as a click, and for IE it will give the user a warning dialog asking them for permission to copy to the clipboard.
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