How to open "incognito" context in puppeteer

puppeteerIncognito.js

"use strict";

const Promise = require('bluebird');
const Page = require('puppeteer/node6/lib/Page');

function newPageWithNewContext(browser) {
  let browserContextId;
  let targetId;
  let target;
  return Promise.resolve()
    .then(() => {
      return browser._connection.send('Target.createBrowserContext');
    })
    .then(res => {
      browserContextId = res.browserContextId;
      return browser._connection.send('Target.createTarget', {url: 'about:blank', browserContextId});
    })
    .then(res => {
      targetId = res.targetId;
      return browser._targets.get(targetId);
    })
    .then(res => {
      target = res;
      return browser._connection.createSession(targetId);
    })
    .then(client => {
      return Page.create(client, target, browser._ignoreHTTPSErrors, browser._appMode, browser._screenshotTaskQueue);
    })
    .then(page => {
      page.__IncoContextData = {
        browserContextId,
        targetId: page._target._targetId
      };
      return page;
    })
    .catch(err => {
      if (browserContextId){
        browser._connection.send('Target.disposeBrowserContext', {browserContextId: browserContextId});
      }
      return Promise.reject(err);
    });
}

function newPageWithExsitingContext(browser, IncoContextData) {
  const {targetId} = IncoContextData;
  let target;
  return Promise.resolve()
    .then(() => {
      return browser._targets.get(targetId);
    })
    .then(res => {
      target = res;
      return browser._connection.createSession(targetId);
    })
    .then(client => {
      return Page.create(client, target, browser._ignoreHTTPSErrors, browser._appMode, browser._screenshotTaskQueue);
    })
    .then(page => {
      page.__IncoContextData = {
        browserContextId: IncoContextData.browserContextId,
        targetId: page._target._targetId
      };
      return page;
    });
}

function closePage(browser, page) {
  let browserContextId;
  if (page.__IncoContextData && page.__IncoContextData.browserContextId) {
    browserContextId = page.__IncoContextData.browserContextId;
  }
  return Promise.resolve()
    .then(() => {
      return page.close();
    })
    .finally(() => {
      if (browserContextId) {
        return browser._connection.send('Target.disposeBrowserContext', {browserContextId: page.__IncoContextData.browserContextId});
      }
    });
}

// browser is the instance returned form puppeteer.launch
module.exports = {
  beginIncognito: browser => {
    return newPageWithNewContext(browser)
      .then(page => {
        page.endIncognito = () => {
          return closePage(browser, page);
        };
        return page;
      });
  },
  addIncognitoTab: (browser, incoPage) => {
    return newPageWithExsitingContext(browser, incoPage.__IncoContextData)
      .then(page => {
        page.endIncognito = () => {
          return closePage(browser, page);
        };
        return page;
      });
  }
};