A JavaScript bundle optimizer.
JavaScript HTML Other
Fetching latest commit…
Cannot retrieve the latest commit at this time.
Failed to load latest commit information.
bin Cleanup files Dec 12, 2017
fb-www Add a guide for debugging React Compiler Apr 27, 2018
flow-libs Set up adapter communication channel with Prepack Oct 27, 2017
flow-typed/npm Replace expensive second babel-traverse pass with fast custom visitor. May 14, 2018
scripts Add ReactDOM.createPortal inlining May 23, 2018
src Fix composePossiblyNormalCompletions to leave abrupt branches alone May 24, 2018
test Add ReactDOM.createPortal inlining May 23, 2018
website Matching end tags Errors fixed May 13, 2018
.babelrc Update webpack and change Babel settings Mar 6, 2018
.eslintignore Tidies up the React mock logic + ReactDOM mocks + few tweaks May 2, 2018
.eslintrc Collect fine-grained statistics on memory usage Apr 27, 2018
.flowconfig Upgrading to Flow .69, starting @flow strict annotations Apr 3, 2018
.gitignore Add React-related internal regression test to Prepack Apr 23, 2018
.gitmodules Initial commit Mar 29, 2017
.watchmanconfig Add React functional component folding Nov 6, 2017
CODE_OF_CONDUCT.md Add COC to Prepack Nov 21, 2017
CONTRIBUTING.md add reading wiki link to places May 13, 2018
LICENSE Initial commit Mar 29, 2017
PATENTS Initial commit Mar 29, 2017
README.md add reading wiki link to places May 13, 2018
circle.yml Special handling for temporal assignments to unknown properties May 1, 2018
package.json 0.2.36-alpha.0 May 21, 2018
webpack.config.js Update webpack and change Babel settings Mar 6, 2018
yarn.lock Update Flow version May 11, 2018


Prepack Circle CI

Prepack is a partial evaluator for JavaScript. Prepack rewrites a JavaScript bundle, resulting in JavaScript code that executes more efficiently. For initialization-heavy code, Prepack works best in an environment where JavaScript parsing is effectively cached.

See the official prepack.io website for an introduction and an interactive REPL playground.

How to use Prepack

Install the CLI via npm,

$ npm install -g prepack

Or if you prefer yarn, make sure you get yarn first,

$ npm install -g yarn

and then install the Prepack CLI via yarn:

$ yarn global add prepack

You may need to prepend (pun intended!) the command with sudo in some cases.

Let the party begin

To compile a file and print the output to the console:

$ prepack script.js

If you want to compile a file and output to another file:

$ prepack script.js --out script-processed.js

Detailed instructions and the API can be found at Prepack CLI: Getting Started

Plugins to other tools

The following are a few plugins to other tools. They have been created and are maintained separately from Prepack itself. If you run into any issues with those plugins, please ask the plugin maintainers for support.


How to get the code

  1. Clone repository and make it your current directory.
  2. git submodule init
  3. git submodule update --init
  4. Get yarn and node, then do yarn

Note: For development work you really need yarn, as many scripts require it.

How to build, lint, type check

  1. Get the code
  2. yarn build
    You can later run yarn watch in the background to just compile changed files on the fly.
  3. yarn lint
  4. yarn flow

How to run tests

  1. Get the code
  2. Make sure the code is built, either by running yarn build or yarn watch
  3. yarn test

You can run individual test suites as follows:

  • yarn test-serializer
    This tests the interpreter and serializer. All tests should pass.
  • yarn test-test262
    This tests conformance against the test262 suite. Not all will pass, increasing conformance is work in progress.

How to run the interpreter

  1. Get the code
  2. Make sure the code is built, either by running yarn build or yarn watch
  3. yarn repl
    This starts an interactive interpreter session.

How to run Prepack

  1. Get the code

  2. Make sure the code is built, either by running yarn build or yarn watch.

  3. Have a JavaScript file handy that you want to prepack, for example:
    echo "function hello() { return 'hello'; } function world() { return 'world'; } s = hello() + ' ' + world();" >/tmp/sample.js

  4. cat /tmp/sample.js | yarn prepack-cli
    Try --help for more options.

How to validate changes

Instead of building, linting, type checking, testing separately, the following does everything together:
yarn validate

How to edit the website

The content for prepack.io resides in the website directory of this repository. To make changes, submit a pull request, just like for any code changes.

In order to run the website locally at localhost:8000:

  1. Build prepack into the website: yarn build-bundle && mv prepack.min.js website/js
  2. Run python -m SimpleHTTPServer (Python 2) or python -m http.server (Python 3) from the website/ directory

How to contribute

To read more about the project, check out this suggested reading wiki

For more information about contributing pull requests and issues, see our Contribution Guidelines.


Prepack is BSD-licensed. We also provide an additional patent grant.