JS实现一键复制文本到剪贴板

function buttonCopyCode(txt){  
    if (window.clipboardData) {  
        window.clipboardData.clearData();  
        window.clipboardData.setData("Text", txt);  
    } else if (navigator.userAgent.indexOf("Opera") != -1) {  
        window.location = txt;  
    } else if (window.netscape) {  
        try {  
            netscape.security.PrivilegeManager  
                    .enablePrivilege("UniversalXPConnect");  
        } catch (e) {  
            alert("你使用的FireFox浏览器,复制功能被浏览器拒绝！\n请在浏览器地址栏输入“about:config”并回车。\n然后将“signed.applets.codebase_principal_support”双击，设置为“true”");  
            return;  
        }  
        var clip = Components.classes['@mozilla.org/widget/clipboard;1']  
                .createInstance(Components.interfaces.nsIClipboard);  
        if (!clip)  
            return;  
        var trans = Components.classes['@mozilla.org/widget/transferable;1']  
                .createInstance(Components.interfaces.nsITransferable);  
        if (!trans)  
            return;  
        trans.addDataFlavor('text/unicode');  
        var str = new Object();  
        var len = new Object();  
        var str = Components.classes["@mozilla.org/supports-string;1"]  
                .createInstance(Components.interfaces.nsISupportsString);  
        var copytext = txt;  
        str.data = copytext;  
        trans.setTransferData("text/unicode", str, copytext.length * 2);