How to: Copy to clipboard with JavaScript

function copyToClipboard(text)
{
    if (window.clipboardData) // Internet Explorer
    {  
        window.clipboardData.setData("Text", text);
    }
    else
    {  
        unsafeWindow.netscape.security.PrivilegeManager.enablePrivilege("UniversalXPConnect");  
        const clipboardHelper = Components.classes["@mozilla.org/widget/clipboardhelper;1"].getService(Components.interfaces.nsIClipboardHelper);  
        clipboardHelper.copyString(text);
    }
}

Automatic copying to clipboard may be dangerous, therefore most browsers (except IE) make it very difficult. Personally, I use the following simple trick:

function copyToClipboard(text) {
  window.prompt("Copy to clipboard: Ctrl+C, Enter", text);
}

The user is presented with the prompt box, where the text to be copied is already selected. Now it's enough to press Ctrl + C and Enter (to close the box) -- and voila!

Now the clipboard copy operation is SAFE, because the user does it manually (but in a pretty straightforward way). Of course, works in all browsers.