Render a webpage and get the image as a stream


Render a webpage and get the image as a stream.

npm install phantom-render-stream

It uses a pool of phantom processes so it doesn't need to spawn a new process for each website. New requests are added to the pool member with the shortest queue length.

This module depends on the phantomjs module, which will install phantomjs for you if you don't already have it.

var phantom = require('phantom-render-stream');
var fs = require('fs');
var render = phantom();
// render a website url 
// or as a transform stream 

You can also pass some options:

var render = phantom({
  pool        : 5,           // Change the pool size. Defaults to 1 
  timeout     : 1000,        // Set a render timeout in milliseconds. Defaults to 30 seconds. 
  tmp         : '/tmp',      // Set the tmp where tmp data is stored when communicating with the phantom process. 
                             //   Defaults to /tmp if it exists, or os.tmpDir() 
  format      : 'jpeg',      // The default output format. Defaults to png 
  quality     : 100,         // The default image quality. Defaults to 100. Only relevant for jpeg format. 
  width       : 1280,        // Changes the width size. Defaults to 1280 
  height      : 800,         // Changes the height size. Defaults to 960 
  paperFormat : 'A4',        // Defaults to A4. Also supported: 'A3', 'A4', 'A5', 'Legal', 'Letter', 'Tabloid'. 
  orientation : 'portrait',  // Defaults to portrait. 'landscape' is also valid 
  margin      : '0cm',       // Defaults to 0cm. Supported dimension units are: 'mm', 'cm', 'in', 'px'. No unit means 'px'. 
  userAgent   : '',          // No default. 
  headers     : {Foo:'bar'}, // Additional headers to send with each upstream HTTP request 
  paperSize:  : null,        // Defaults to the paper format, orientation, and margin. 
  crop        : false,       // Defaults to false. Set to true or {top:5, left:5} to add margin 
  printMedia  : false,       // Defaults to false. Force the use of a print stylesheet. 
  maxErrors   : 3,           // Number errors phantom process is allowed to throw before killing it. Defaults to 3. 
  expects     : 'something', // No default. Do not render until window.renderable is set to 'something' 
  retries     : 1,           // How many times to try a render before giving up. Defaults to 1. 
  phantomFlags: ['--ignore-ssl-errors=true'] // Defaults to []. Command line flags passed to phantomjs 
  maxRenders  : 20,          // How many renders can a phantom process make before being restarted. Defaults to 20 
  injectJs    : ['./includes/my-polyfill.js'] // Array of paths to polyfill components or external scripts that will be injected when the page is initialized 

Or override the options for each render stream

render(myUrl, {format:'jpeg', quality: 100, width: 1280, height: 960}).pipe(...)

We support the output formats that Phantom's render method supports. At the time of this writing these are:

  • png
  • gif
  • jpg
  • pdf

Since the interface is just a stream you can pipe the web site anywhere! Try installing picture-tube and run the following example

var phantom = require('phantom-render-stream');
var pictureTube = require('picture-tube');
var render = phantom();

If you need your page to do something before phantom renders it you just need to immediately set window.renderable to false. If that is set when the page is opened the module will wait for window.renderable to be set to true and when this happens the render will occur.

Here is an example to illustrate it better.

<html lang="en">
  <script type="text/javascript">window.renderable = false</script> 
  <meta charset="UTF-8">
<script type="text/javascript">
  doSomeAjaxLoading(function() {
    window.renderable = true;

You can add any special cookies at render time. For format, see Example:

var render = phantom({
  pool: 5,
  format: 'pdf'
  // other opts 
render('', {
  cookies: [{
    'name'     : 'Valid-Cookie-Name',   /* required property */
    'value'    : 'Valid-Cookie-Value',  /* required property */
    'domain'   : 'localhost',
    'path'     : '/foo',                /* required property */
    'httponly' : true,
    'secure'   : false,
    'expires'  : (new Date()).getTime() + (1000 * 60 * 60)   /* <-- expires in 1 hour */

That will use that cookie for that particular render job. You probably want to set the expires property to something fairly short, as there may not be a guarantee that a pooled phantom process won't pick up the cookie for a particular render job, and you may want that session to only be valid for an individual job run.

Sometimes you need to inject polyfills, e.g. PhantomJS Date.parse is broken. You can add paths to local files to polyfill broken / missing features of PhantomJS using the opts.injectJs property. Example:

var phantom = render({
  injectJs: ['./includes/my-date-polyfill.js']

Obviously, make sure the path './includes/my-date-polyfill.js' is resolvable from the project root, or pass in an absolute path. When the page is initialized, any scripts you listed there will be injected before any rendering happens.

For rendering, PhantomJS requires the fontconfig library, which may be missing if you're using Ubuntu Server. To install on Ubuntu:

sudo apt-get install libfontconfig

Some additional debugging output may be enabled by running your script with a DEBUG environment variable set as follows:

DEBUG=phantom-render-stream  node ./your-script.js

If you are getting undefined error codes and responses when attempting to render, it's likely a connection issue of some sort. If the URL uses SSL, adding --ignore-ssl-errors=true to phantomFlags may help. You also try adding --debug=true to the phantomFlags array.

  • wkhtmltopdf is a Node module that uses wkhtmltopdf to convert HTML to PDF. It is similar in that it uses Webkit and produces output as a stream, and different in that it doesn't use PhantomJS. Also, wkhtmotopdf only supports PDF output.