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！") ;
}