Issue 4795 - Use modern JavaScript syntax

composer.js

 /*
  * This file is part of Adblock Plus <https://adblockplus.org/>,
  * Copyright (C) 2006-2016 Eyeo GmbH
  *
  * Adblock Plus is free software: you can redistribute it and/or modify
  * it under the terms of the GNU General Public License version 3 as
  * published by the Free Software Foundation.
  *
  * Adblock Plus is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  * GNU General Public License for more details.
  *
  * You should have received a copy of the GNU General Public License
  * along with Adblock Plus.  If not, see <http://www.gnu.org/licenses/>.
  */
 
-var targetPageId = null;
+let targetPageId = null;
 
 function onKeyDown(event)
 {
   if (event.keyCode == 27)
   {
     event.preventDefault();
     closeDialog();
   }
   else if (event.keyCode == 13 && !event.shiftKey && !event.ctrlKey)
   {
     event.preventDefault();
     addFilters();
   }
 }
 
 function addFilters()
 {
   ext.backgroundPage.sendMessage(
   {
     type: "filters.importRaw",
     text: document.getElementById("filters").value
   },
-  function(errors)
+  errors =>
   {
     if (errors.length > 0)
       alert(errors.join("\n"));
     else
       closeDialog(true);
   });
 }
 
 function closeDialog(success)
 {
@@ skipping 18 matching lines @@
   document.getElementById("addButton").addEventListener("click", addFilters);
   document.getElementById("cancelButton").addEventListener(
     "click", closeDialog.bind(null, false)
   );
 
   // Apply jQuery UI styles
   $("button").button();
 
   document.getElementById("filters").focus();
 
-  ext.onMessage.addListener(function(msg, sender, sendResponse)
+  ext.onMessage.addListener((msg, sender, sendResponse) =>
   {
     switch (msg.type)
     {
       case "composer.dialog.init":
         targetPageId = msg.sender;
         document.getElementById("filters").value = msg.filters.join("\n");
         break;
       case "composer.dialog.close":
         window.close();
         break;
     }
   });
 
   window.removeEventListener("load", init);
 }
 window.addEventListener("load", init, false);