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0.0.7 • Public • Published

Browser Client


Remote management client for browsers supporting the Chrome DevTools Protocol, built to be easy to use. And further than that, be ready for production use. Currently being battle-tested over at Passmarked before we launch.

We've been quite excited about the developments allowing us to better use Chrome and move away from PhantomJS (which has an ever ageing version of WebKit). After following the announcements we wanted to get ready for the switch and started building a library we would able to use in our production setup.

We set out with a few goals:

  • Learn from PhantomJs which we have been using for over a year now and address issues we had.
  • Layout the API in a way similar to a simple HTTP client like request to reduce the barrier of entry for everyone.
  • Built from the ground up to support parallel processing and keeping a long running instance sane by cleaning up every chance it gets.
  • Built-in configurable queueing to make it easy to build systems that won't fall over once traffic starts hitting.
  • Keeping it generic enough to use multiple browsers supporting the same protocol.
  • Build generic convenience methods to get information users are normally interested in. Such as building a HAR, taking screenshots, emulation and in page code execution (much like PhantomJs).

Join our Slack channel to join the conversation and help us build this out.


As you might know, tonnes of features like the --headless feature from Chrome is still only in Canary. It will be released to the mainline stream in the next release. With a growing list of features following.

Development Status

Currently building out and figuring out the API, will be ready for use in the next week. The current release does work, API might just be tweaked a bit after usage.


  • Add samples
  • Add proper logging with options
  • Add testing suite [IN PROGRESS]
  • Testing after integration with our live system

Current version - 0.0.6

Production Status

The module is currently being tested for use in our website testing suite at Passmarked, which we hope to have out of beta in the next few weeks and running Chrome in headless mode. Expect tonnes of updates and performance enhancements.

Join our Slack channel to join the conversation and help us build this out.


Install the module

To install the module use either NPM or Yarn:

npm install [-g] [--save] @passmarked/browser


yarn install add [--save] @passmarked/browser

Run an instance of browser

To use the library we need a browser instance we can connect to. As of writing this (6 May 2017) --headless is only available in Canary along with most of the required features to run the library. So first download and install Chrome Canary.

Different Operating Systems will install the executable to separate locations (unless done manually). On Mac OS (by default) this is /Applications/Google\ Chrome\\ Chrome\ Canary

Then run using:

google-chrome-canary [--headless] --disable-gpu --remote-debugging-port=9222

Using --headless will allow a server to run an instance of the browser, or simply on your desktop without showing an actual browser. No xvfb needed!

Notable mentions:

  • It seems at the moment Chrome only allows connections from localhost, (being careful of course, really careful ...) you can open up to an external IP using a reverse proxy like NGINX. See samples/nginx.conf for a sample NGINX config.
  • For security reasons Chrome does not return the amount of memory being used precisely. To enable and use the page.getMemory() function, add --enable-precise-memory-info.
  • For now --disable-gpu is required in --headless mode as issues are being sorted out.


As an example, to get you up and running quickly, here how to save a screenshot of

// Gotta start somewhere !
const fs = require('fs');
const Browser = require('@passmarked/browser')
* Create a client context that will be used to access
* the remote browser instance. Supplying the host
* and port of the remote instance to connect to.
var client = Browser({
  host:    'localhost', // default host
  port:    9222, // default port
* Load a page with the specified URL and options.
* See #Options for all possible config options.
  url: '',
  background: '#fff', // default background to white
  timeout: 30 * 1000 // 30 second timeout
}, function(err, page) {
  // check for an error related to the remote instance connection
  if(err) {
    // debugging message
    console.log('failed to connect');
    // output the error
    // done
  // get the result of the connection
  var result = page.getResult();
  // check if we were able to load
  if(result != 'success') {
    // output the result
    console.log('Problem loading page: ' + result);
    // close the page context to allow next page
    // to run in queue -- see #tabs under #Options
    // finish up
  // render pdf
    format:      'png' // pdf, png or jpeg
  }, function(err, buf) {
    // check for error
    if(err) {
      // nope ...
      console.log('file write failed :(');
      // done
      return page.close();
    // write the buffer to file
    fs.writeFile('output.png', buf, function() {
      // close the context
      // done
      console.log('loaded, and writen to output.pdf')


Various options are provided which control how the library interacts with the browser and what the tab itself will look like (IE emulation/width/height etc).

Browser Options

These options apply only when creating a browser client:

  • host - Host where the remote instance of Chrome is running - default is localhost
  • port - Port where the remote instance is running - default is 9222
  • tabs - Maximum number of tabs to run in parallel - default is 1

Browser/Page Options

Options that can be applied to pages being loaded which control how it looks/feels. Options can be supplied to both the browser and the .load() function, where .load() will default to the browser options and will override when passed anything in the .load() the method itself.

  • url - URL to load
  • timeout - Number of ms before stopping and returning a "timeout" error - default no limit
  • disableCache - TRUE/FALSE to enable or disable cache - default FALSE
  • bypassServiceWorkers - TRUE/FALSE to enable or disable server worker cache - default FALSE
  • ignoreSSL - TRUE/FALSE to return of any SSL verification - default TRUE
  • userAgent - String of user agent to use when sending request - default set by system/browser
  • cpu - Trottle the cpu, number from 1 up. 1 = normal speed, 2=x2 slower. And so on.
  • downloadRate - Trottle the speed of network in bytes
  • uploadRate - Trottle the speed of network in bytes
  • latency - Amount of latecy to add to each request
  • offline - Emulate the network being offline
  • connectionType - Emulate a network type (packet drops and latency fluctuations) = 2g, 3g, adsl
  • width - Width of tab (viewport)
  • height - Height of tab (viewport)
  • mobile - TRUE/FALSE to emulate mobile behavior
  • scale - Adjust the scale factor for mobile, default=1
  • orientation - Adjust the orientation of the tab, could be portraitPrimary, portraitSecondary, landscapePrimary, landscapeSecondary
  • media - Emulate a media for @media queries - IE 'print'
  • recordEvery - Record a screenshot every supplied ms - IE 100 for every 100ms
  • headers - Map of headers to send with request
  • cookies - Cookies to send in request


There are a few important calls that are needed to work with the library:


Creates a client that will allow you to load pages.

const Browser = require('@passmarked/browser');
var browser = Browser({ ... options ... });

Options provided for the browser will be the default for all pages loaded in that browser, unless overridden by the .load() calls them.

The browser client does not maintain a connection to Chrome instances, rather it simply saves the options and connects as needed. Each page context is a web socket connection being used to control the remote browser.

browser.load(options, fn)

Creates a page context that can be interacted with. When created the context is assigned to a tab in the browser, and as per configurations (see #tabs under #Options) .load() calls exceeding the currently executing tabs will block till a tab is available.

browser.load({ ... options ... }, function(err, page) {
    page <- the context for the page

The function will use any options defined when creating the browser connection, but any of those options can also be overridden here:

browser.load({ ... options ... }, function(err, page) {
    page <- the context for the page


Closes the context and adds the tab back to pool, which will cause the next URL specified to load. This must be called to continue processing once you are done with a page. The function also handles cleaning up and closing the connections while flushing stale tabs once they idle again.



Returns the result of trying to connect to the specified URL which is either:

  • success - All is good. Was able to connect and found a document to respond. Not to be confused with HTTP status. This could be any status code just as long as we are able to load the page in Chrome without connection problems.
  • insecure - There was an issue connecting due to HTTPS/SSL - see #ignoreSSL under #Options to disable checking
  • timeout - The configured timeout was exceeded
  • failed - We are just not able to connect to the specified URL

Page Functions

The module also provides quite a few convenience functions that can be accessed once a page context has to be retrieved:


Returns the final URL (supports Pushstate as well) of the page:

page.getURL(function(err, url) { 


Returns a list of all websockets connections that took place:

page.getTrackedWebsockets(function(err, websockets) { 


Returns a list of all frames sent and received over websocket connections:

page.getTrackedWebsocketFrames(function(err, frames) { 


Returns a list of all console messages along with severity logged to the javascript console

page.getConsoleMessages(function(err, messages) { 


Returns a list of javascript dialogs encountered while loading the page along with text and type (prompt/alert)

page.getJavascriptDialogs(function(err, dialogs) { 


Returns the navigation history of documents that led to the final doc:

page.getNavigationHistory(function(err, documents) { 


Returns the raw request/response for the final page document:

page.getDocument(function(err, doc) { 


Returns the memory usage of the Heap in bytes.

page.getMemoryUsage(function(err, memory) { 
  console.log((memory / 1024) + 'kb used'); 

page.render(params, fn)

Renders out the page in various formats, with options to emulate various sizes and devices:

    format: 'png', // REQUIRED - jpeg, png or pdf
    quality: 30, // OPTIONAL - quality of jpeg produced, default 100
    // OPTIONAL Emulation Settings
    width: 320, // width of page
    height: 420, // height of page - null = till the bottom
    scale: 1, // scale factor of viewport
    orientation: 'portraitPrimary',
    media: 'print', // emulate a @media query media
}, {
  hello: 'world' // params to pass
}, function(err, value) {
  console.log(value); //

page.exec(functionToExec, params, fn)

Runs the specified javascript in the context of the page itself.

Handles serializing the javascript, sending arguments and retrieving the response.

Supports returning values/objects or just nothing.

page.exec(function(params) { 
  return document.location.toString()
}, {
  hello: 'world' // params to pass
}, function(err, exception, value) {
  console.log(value); //


Returns the requests/responses formatted according to the HAR specification:

page.getHAR(function(err, har) { 


Returns the content (after executing javascript) of the page:

page.getContent(function(err, content) { 


Returns the total size of the page in bytes:

page.getSize(function(err, size) { 


Returns the total time it took for the page to load in ms:

page.getDuration(function(err, duration) { 


Copyright 2017 Passmarked Inc

Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at

Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.


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