NPM Package modification with patch-package

When working with open-source projects and npm packages, sometimes there are minor tweaks or bug fixes you want to make without going through the entire pull request process. That's where patch-package comes in, a handy tool I learned about today.

Patch-package lets you modify an npm package in your node_modules directory, then creates a .patch file that you can commit to your project's source control. Essentially, you can keep a record of the modifications and apply them whenever you reinstall or update your node modules. This tool is a great way to manage necessary changes without directly altering the original package code.

You can simply make changes in the package code in your node_modules, and then run npx patch-package <package_name> to create a patch file. Later, you can apply this patch using npx patch-package during the installation process in your postinstall script. This ensures that your changes persist across different environments or after a fresh install.

Navigate to the package code in your node_modules folder and make your changes. For instance:


// node_modules/some-package/index.js
exports.someFunction = function() {
    // Original implementation
    // ...

    // Modified implementation
    console.log('Function has been patched');
    // ...
}

After making your modifications, you need to create a patch. From the root directory of your project, you can run the following command:


npx patch-package some-package

This will create a file in a directory called patches with a name like some-package+0.0.1.patch.

Then, you'll need to make sure this patch gets applied every time your project is installed. In your package.json, you'll add a postinstall script:


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

Now, every time you or someone else installs your project with npm install, your modifications to some-package will be applied!