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Mobify.js is an open source library for improving the performance of websites by providing responsive images, and optimized JS/CSS. It does this by using capture.js to control the resources on the page, and uses resizeImages.js, jazzcat.js, and cssOptimize.js to change the resources on the page to point to Mobify's proxy services to optimize the resources.

For instructions on how to use the library, follow the instructions on or build the docs site manually in the instructions below.



Mobify.js uses Bower, Grunt.js and Require.js to build the library, and manage all of the dependencies. First, you will need to install the grunt-cli globally:

npm install -g grunt-cli

And then download the latest code from git and install the dependancies:

git clone
cd mobifyjs
npm install
bower install

Now, to build the library, simply run the following command:

grunt build

Open the build folder to see the generated Mobify.js libraries.

Mobify.js is built with AMD modules using almond.js.

In order to build Mobify.js during development without having to run grunt build everytime you change a file, run the following command:

grunt serve

This will run a development server on http://localhost:3000 using connect, and build the library every time the files in src change.

To see how the project is setup to build, open up Gruntfile.js and have a look!

Build Setup

Require.js is used to build Mobify.js.

  • src/config.js # The require.js base config for all build mobify.js builds
  • src/mobify-library.js # Defines how to build the full mobify.js library

There is also an example custom build file to make it simple to build a custom mobify.js library (or to compile the library with executable code):

  • mobify-custom.js.example

To create a custom build, run the following:

`cp mobify-custom.js.example mobify-custom.js`

Then, run grunt serve as normal. The output of the custom build will be located in build/custom.

Note: We use a mobifyjs symlink to resolve paths so they can be the same locally as they are on the CDN. This can be problematic for Windows.


Tests for Mobify.js are written in QUnit. To run them individually, run grunt serve and then go to http://localhost:3000/tests/capture.html or any other of the QUnit tests in the /tests/ folder.

To run all of the tests in an automated fashion using Phantomjs (the headless webkit browser) run the following command:

grunt test

It's also important when developing not to run into any regressions on all of the supported browsers. The Gruntfile is setup to be able to run qunit tests on many browsers we support (in order to do this yourself, you will need to set SAUCE_USERNAME and SAUCE_KEY in your environment variables).

grunt saucelabs


By default, the deploy command is set to deploy Mobify.js to To deploy here, ensure AWS_ACCESS_KEY_ID and AWS_SECRET_ACCESS_KEY are set in your environment variables.

grunt deploy

Browser support

Using Capturing:

  • All Webkit browsers (Safari, Chrome, Netfront, etc)
  • Firefox - version 4 and up
  • Opera - 11 and up (previous versions untested)
  • IE - 10 and up

Not Using Capturing:

Support for using the API without Capturing has not been tested, but it will at minimum support the browsers listed above (as well, it should cover many older browsers)


The compiled documentation for Mobify.js can be found online at

The static site is built with Jekyll. Run the following commands to get the docs running locally:

gem install jekyll
grunt jekyll

Then navigate to http://localhost:4000/mobifyjs/docs/.


Mobify.js was a JavaScript framework for optimizing sites for mobile. It is no longer actively maintained.




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