JS复制网页上的内容到剪切板

function copyToClipboard(txt) {
    if(window.clipboardData) {
      window.clipboardData.clearData();
      window.clipboardData.setData("Text", txt);
      alert("Your request has been processed successfully.");
    } 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("Your request has been processed successfully.");
    }
   }