A light-weight JS build tool


Often when deploying JS components, you want to compile a multitude of source files down to a single build result. The benefits of doing this include faster performance from the client perspective (due to fewer http hits to load scripts), and potentially simpler integration by the developer integrating your component. Gravity was specifically designed to ease this process.

gravity is a command-line tool that reads files.

A is a JSON file that can be thought of as a project manifest. In it, you can specify build targets, and the source files that are used to create each target.

    "final.js": [

This tells gravity that you want a build product called final.js, and that it should be the result of compiling various source files (or even other build products) together.

Full documentation of syntax can be found in the file.



  • node 0.6 or greater
  • git 1.7 or greater

To install to ~/git/gravity

mkdir ~/git
cd ~/git
git clone git://
cd gravity
git submodule update --init

Of course you can check it out wherever you like. Just make sure you add the gravity dir (in this example ~/git/gravity) to your path.


Mac/unix/cygwin users will be able to invoke "gravity" directly. To run the commands in Windows cmd.exe, just prepend "node " to the commands below.

To see a list of all the build products, where <dir> is the location of your project's directory (ie., wherever the file is):

gravity list <dir>

During development, you can run gravity as a local server that will perform on-the-fly concatenation of your source.

gravity serve <dir>

The server should find an available local port to attach to, and will announce itself:

Gravity server running on

Now you can visit to see the results. Edit a source file, then refresh the page to see the change instantly!

If you want your gravity server to bind to a specific host or port, you can specify those. Can also be run as a background process.

gravity serve <dir> <host>:<port> &

Come build time, run a command like this:

gravity build <dir> <outdir>

Gravity will take only your build targets and put them into <outdir>.

If you just want to see a specific build target produced and dumped to stdout, you can do this:

gravity pull <dir> final.js

Unit Tests

node test.js // Run unit tests silently
node test.js -v // Run unit tests verbosely