chrome webrequest onBeforeRequest example

background.js

// Copyright (c) 2012 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

// Simple extension to replace lolcat images from
// http://icanhascheezburger.com/ with loldog images instead.

chrome.webRequest.onBeforeRequest.addListener(
  function(info) {
    console.log("Cat intercepted: " + info.url);
    // Redirect the lolcal request to a random loldog URL.
    var i = Math.round(Math.random() * loldogs.length);
    return {redirectUrl: loldogs[i]};
  },
  // filters
  {
    urls: [
      "https://i.chzbgr.com/*"
    ],
    types: ["image"]
  },
  // extraInfoSpec
  ["blocking"]
);

hey
how can i get header request before send
pls simple exm if u can
tnx