Yarn workspace + lerna is creating node_modules in each sub-package

Question

I have a monorepo which I'm managing with yarn workspaces + lerna. From what I understand, running yarn should create a node_modules directory at the root of the project but not in each individual package. I was following a tutorial where the author says this:

yarn workspaces creates only one node_modules folder. All dependencies are hoisted to the root folder

Is this assumption always true? Or is there a case where yarn + lerna will create individual node_modules directories in each package?

Suppliant

Answer 1

I read a few articles and was confused with the same thing.

The short answer is, you are right. Yarn creates node_modules for each package along with a node_modules directory in the root of your repo.

In other words, Yarn creates /packages/<package>/node_modules in all your packages. However, the /packages/<package>/node_modules directory will be optimized by reusing dependencies that are in /node_modules. This is basically what these authors are trying to say!

To sum it up, you will have n + 1 node_modules directories, where n is the number of packages you have, assuming all your packages have dependencies.

Let's consider an example:

yarn workspace package-1 add commander

would not create /packages/package-1/node_modules/commander if it's already in /node_modules/commander with compatible versions.

Now let's look at another case:

yarn workspace package-1 add chalk

If Yarn cannot reuse what's in /node_modules, it will install the package locally, which in our case is /packages/package-1/node_modules/chalk.

You can read more about this in Yarn's official blog: https://classic.yarnpkg.com/blog/2017/08/02/introducing-workspaces/

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