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.
We, the Prepack team at Facebook, have temporarily set down work on Prepack including the React compiler project. You won't see many Prepack PRs while we are currently prioritizing some other projects. However, we'd like to resume work on Prepack again in a few months.
Install the CLI via npm,
$ npm install -g prepackOr if you prefer yarn, make sure you get yarn first,
$ npm install -g yarnand then install the Prepack CLI via yarn:
$ yarn global add prepackYou may need to prepend (pun intended!) the command with sudo in some cases.
To compile a file and print the output to the console:
$ prepack script.jsIf you want to compile a file and output to another file:
$ prepack script.js --out script-processed.jsDetailed instructions and the API can be found at Prepack CLI: Getting Started
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.
- A Rollup plugin for Prepack
- A Webpack plugin for Prepack
- A Parcel plugin for Prepack
- A Visual Studio code plugin for Prepack
- A babel plugin which transforms Flow annotations into prepack model declarations.
- 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.
- Clone repository and make it your current directory.
git submodule initgit submodule update --init- Get yarn and node, then do
yarn
Note: For development work you really need yarn, as many scripts require it.
- Get the code
yarn build
You can later runyarn watchin the background to just compile changed files on the fly.yarn lintyarn flow
- Get the code
- Make sure the code is built, either by running
yarn buildoryarn watch 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.
- Get the code
- Make sure the code is built, either by running
yarn buildoryarn watch yarn repl
This starts an interactive interpreter session.
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Get the code
-
Make sure the code is built, either by running
yarn buildoryarn 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 -
cat /tmp/sample.js | yarn prepack-cli
Try--helpfor more options.
Instead of building, linting, type checking, testing separately, the following does everything together:
yarn validate
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:
- Build prepack into the website:
yarn build && mv prepack.min.js website/js - Run
python -m SimpleHTTPServer(Python 2) orpython -m http.server(Python 3) from thewebsite/directory
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.