patch-package

patch-package lets app authors instantly make and keep fixes to npm
dependencies. It's a vital band-aid for those of us living on the bleeding edge.

# fix a bug in one of your dependencies
vim node_modules/some-package/brokenFile.js

# run patch-package to create a .patch file
npx patch-package some-package

# commit the patch file to share the fix with your team
git add patches/some-package+3.14.15.patch
git commit -m "fix brokenFile.js in some-package"

Patches created by patch-package are automatically and gracefully applied when
you use npm(>=5) or yarn.

No more waiting around for pull requests to be merged and published. No more
forking repos just to fix that one tiny thing preventing your app from working.

Set-up

In package.json

 "scripts": {
+  "postinstall": "patch-package"
 }

Then

npm

npm i patch-package

You can use --save-dev if you don't need to run npm in production, e.g. if
you're making a web frontend.

yarn

yarn add patch-package postinstall-postinstall

You can use --dev if you don't need to run yarn in production, e.g. if you're
making a web frontend.

To understand why yarn needs the postinstall-postinstall package see:
Why use postinstall-postinstall

yarn workspaces

Same as for yarn ☝️ Note that if you want to patch un-hoisted packages you'll
need to repeat the setup process for the child package. Also make sure you're in
the child package directory when you run patch-package to generate the patch
files.

CI

• Gitlab Docker builds, see
  #185

• If you cache node_modules rather than running yarn install every time,
  make sure that the patches dir is included in your cache key somehow.
  Otherwise if you update a patch then the change may not be reflected on
  subsequent CI runs.

  e.g. for cirlce ci before loading/saving you cache run cat patches/*, md5 > patches.hash and then update your hash key to include a checksum of that file, {{ checksum "yarn.lock" }}-{{ checksum "patches.hash" }}

Usage

Making patches

First make changes to the files of a particular package in your node_modules
folder, then run

yarn patch-package package-name

or use npx (included with npm > 5.2)

npx patch-package package-name

where package-name matches the name of the package you made changes to.

If this is the first time you've used patch-package, it will create a folder
called patches in the root dir of your app. Inside will be a file called
package-name+0.44.0.patch or something, which is a diff between normal old
package-name and your fixed version. Commit this to share the fix with your
team.

Options

• --use-yarn

  By default, patch-package checks whether you use npm or yarn based on which
  lockfile you have. If you have both, it uses npm by default. Set this option
  to override that default and always use yarn.

• --exclude <regexp>

  Ignore paths matching the regexp when creating patch files. Paths are relative
  to the root dir of the package to be patched.

  Default value: package\\.json$

• --include <regexp>

  Only consider paths matching the regexp when creating patch files. Paths are
  relative to the root dir of the package to be patched.

  Default value: .*

• --case-sensitive-path-filtering

  Make regexps used in --include or --exclude filters case-sensitive.

• --patch-dir

  Specify the name for the directory in which to put the patch files.

Nested packages

If you are trying to patch a package at, e.g.
node_modules/package/node_modules/another-package you can just put a /
between the package names:

npx patch-package package/another-package

It works with scoped packages too

npx patch-package @my/package/@my/other-package

Updating patches

Use exactly the same process as for making patches in the first place, i.e. make
more changes, run patch-package, commit the changes to the patch file.

Applying patches

Run patch-package without arguments to apply all patches in your project.

Options

• --reverse

  Un-applies all patches.

  Note that this will fail if the patched files have changed since being
  patched. In that case, you'll probably need to re-install node_modules.

  This option was added to help people using CircleCI avoid
  an issue around caching and patch file updates
  but might be useful in other contexts too.

• --patch-dir

  Specify the name for the directory in which the patch files are located

Notes

To apply patches individually, you may use git:

git apply --ignore-whitespace patches/package-name+0.44.2.patch

or patch in unixy environments:

patch -p1 -i patches/package-name+0.44.2.patch

Dev-only patches

If you deploy your package to production (e.g. your package is a server) then
any patched devDependencies will not be present when patch-package runs in
production. It will happily ignore those patch files if the package to be
patched is listed directly in the devDependencies of your package.json. If
it's a transitive dependency patch-package can't detect that it is safe to
ignore and will throw an error. To fix this, mark patches for transitive dev
dependencies as dev-only by renaming from, e.g.

package-name+0.44.0.patch

to

package-name+0.44.0.dev.patch

This will allow those patch files to be safely ignored when
NODE_ENV=production.

Benefits of patching over forking

• Sometimes forks need extra build steps, e.g. with react-native for Android.
  Forget that noise.
• Get told in big red letters when the dependency changed and you need to check
  that your fix is still valid.
• Keep your patches colocated with the code that depends on them.
• Patches can be reviewed as part of your normal review process, forks probably
  can't

When to fork instead

• The change is too consequential to be developed in situ.
• The change would be useful to other people as-is.
• You can afford to make a proper PR to upstream.

Isn't this dangerous?

Nope. The technique is quite robust. Here are some things to keep in mind
though:

• It's easy to forget to run yarn or npm when switching between branches
  that do and don't have patch files.
• Long lived patches can be costly to maintain if they affect an area of code
  that is updated regularly and you want to update the package regularly too.
• Big semantic changes can be hard to review. Keep them small and obvious or add
  plenty of comments.
• Changes can also impact the behaviour of other untouched packages. It's
  normally obvious when this will happen, and often desired, but be careful
  nonetheless.

Why use postinstall-postinstall with Yarn?

Most times when you do a yarn, yarn add, yarn remove, or yarn install
(which is the same as just yarn) Yarn will completely replace the contents of
your node_modules with freshly unpackaged modules. patch-package uses the
postinstall hook to modify these fresh modules, so that they behave well
according to your will.

Yarn only runs the postinstall hook after yarn and yarn add, but not after
yarn remove. The postinstall-postinstall package is used to make sure your
postinstall hook gets executed even after a yarn remove.

License

MIT