兼容IE FF Opera的 JS复制方法

function copyToClipboard(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("被浏览器拒绝！请在浏览器地址栏输入'about:config'并回车 然后将'signed.applets.codebase_principal_support'设置为'true'");            }            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);            var clipid = Components.interfaces.nsIClipboard;            if (!clip)                 return false;            clip.setData(trans,null,clipid.kGlobalClipboard);       }    alert("复制成功！") ;}