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.

Status

test262 status on master branch
code coverage report for serialization tests
To see the status for a pull request, look for the message All checks have passed or All checks have failed. Click on Show all checks, Details, Artifacts, and then test262-status.txt or coverage-report-sourcemapped/index.html.

How to get the code

Clone repository and make it your current directory.
git submodule init
git submodule update --recursive --remote
Get npm and node, then do npm install

How to build, lint, type check

Get the code
npm run build
You can later run npm run watch in the background to just compile changed files on the fly.
npm run lint
npm run flow

How to run tests

Get the code
Make sure the code is built, either by running npm run build or npm run watch
npm test

You can run individual test suites as follows.

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

How to run the interpreter

Get the code
Make sure the code is built, either by running npm run build or npm run watch
npm run repl
This starts an interactive interpreter session.

How to run Prepack

Get the code
Make sure the code is built, either by running npm run build or npm run watch.
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
npm run prepack /tmp/sample.js
Try --help for more options.

How to validate changes

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

How to edit the website

The content for prepack.io resides in the gh-pages branch 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, run python -m SimpleHTTPServer from the cloned gh-pages branch.

At this time, a particular bundled version of Prepack is checked in to the gh-pages branch at js/prepack.min.js. To update the bundle, run npm run build-bundle from the master branch, and copy the resulting prepack.min.js file into the gh-pages branch into the js directory, and submit a pull request for that change.

How to contribute

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

License

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