Nx

Lerna is a monorepo tool that’s been around for a while. There was a period of time where it was basically abandoned, and it has since been maintained by the Nx team. We’ll look at what Lerna can do for us, and then we’ll see when it’s appropriate to use Nx directly instead.

Lerna

Run

sh
pnpm dlx lerna init

You should then be able to run

sh
pnpm lerna run build

Which will build every package in the monorepo. You can similarly run

sh
pnpm lerna run test
pnpm lerna run lint

You can run multiple tasks

sh
pnpm lerna run build,lint,test,check

You can stream output

sh
pnpm lerna run build,lint,test,check --stream

You can control the degree of parallelism

sh
pnpm lerna run build,lint,test,check --concurrency=2

Or unlimited concurrency

sh
pnpm lerna run build,lint,test,check --parallel

—since

A lot of the task running can be accomplished with pnpm (although it’s a bit more convoluted), however lerna is much more sophisticated. It can run tasks based on changes relative to a given git ref (e.g. a branch).

Change the logging message in packages/server/src/index.ts

diff
-  console.log(`Server listening on port http://localhost:${cfg.port}`)
+  console.log(`Listening on port http://localhost:${cfg.port}`)

Now run

sh
pnpm lerna run test --since=origin/steps-2

and you should see that only tests in the @seeds/server package are run. If you make a change within the @seeds/model package, you should see that tests in all three packages are run because of the dependency graph.

Particularly if you’re thinking about git pre-commit hooks (e.g. if you’re using husky), this is a great foundational feature that lets you operate on the increment of code change while taking the dependency graph within the monorepo into account.

Nx

Let’s go deeper and explore using Nx directly.

Install nx globally

sh
npm add --global nx
# OR
volta install nx

And install it in the root of the repo

sh
pnpm dlx nx init

Follow the prompts to create a nx.json file

At the end of the process we should benefit from distributed caching. As long as the inputs to cachable build tasks are the same, the output should be the same and the response is pretty much instantaneous. This can dramatically speed up your build process.

sh
nx run-many -p models,ui,server,check -t build,lint,test