Simultaneously Working on Application and Dependency
Sometimes you need to work on application code and a dependency at the same time. You might be the author of a dependency and don’t have good test coverage yet. The application can serve as an end-to-end test for the dependency. Maybe you need to debug an issue in your application and the problem seems to be in the dependency sources.
You could make changes in
node_modules and manually copy the changes to the
git repository of the dependency once you are done. But there is a much cleaner approach:
Package linking is a two-step process:
- Create a global symlink for a dependency with
npm link. A symlink, short for symbolic link, is a shortcut that points to another directory or file on your system.
- Tell the application to use the global symlink with
npm link some-dep.
cd ~/projects/some-dep npm link # Step 1. cd ~/projects/my-app npm link some-dep # Step 2.
You can edit, transpile, run tests, or commit as usual in
some-dep. All while
my-app runs with the changes you made to
some-dep. The symbolic links are local and will not be committed to
git. When you are ready to share your code, publish a new version of
some-dep or push to a branch that you specify in
cd ~/projects/my-app npm install — save some-dep@fhinkel/some-dep#experimental-branch
If you use VSCode and want to set breakpoints in
some-dep, you need to enable symlinks in the debugger for
my-app. Do so by setting
“runtimeArgs”: [ “--preserve-symlinks” ]
Back to Normal
How do you switch back to normal dependencies? When you don’t want to use the local version of
some-dep anymore, delete the symlink. But careful,
npm unlink is an alias for
npm uninstall, it does not mirror the behavior of
cd ~/projects/my-app npm uninstall --no-save some-dep && npm install
You can clean up the global link, though its presence won’t interfere with
cd ~/projects/some-dep npm uninstall # Delete global symlink
npm link while working on dependencies of the client libraries for Google Cloud Platform. All our libraries use the module
@google-cloud/common. In some cases I needed to immediately see the changes in the larger libraries instead of in isolation in
Mastering the two-step process of
npm link is a useful addition to the toolset of any Node.js developer. The process consists of running
npm link in the dependency, and
npm link some-dep in the application.
Huge thanks to Peter Marshall and Alexander Fenster for helping review this post.