拷贝文字到剪贴板firefox ie 通用js函数

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！\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'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！")        

      }        

}