Don't use SWC when you're using Nestjs Monorepo

Overview

There was a release of version 10 in Nest.js this June.

There were some changes like

• Simple SWC support
• Module overriding feature in testing
• Redis wildcard subscription
• CacheModule separated from @nestjs/common to @nestjs/cache-manager

But, We're only going to talk about SWC

SWC Integration

npm i --save-dev @swc/cli @swc/core
nest start -b swc

That's all you need to do to use SWC.
It's lightning fast when you use in standard mode.

In Monorepo

When It comes to Monorepo, It's not.

Nest.js provides monorepo mode.
Let's Try SWC.

// nest-cli.json
{
  "compilerOptions": {
    "builder": "swc", // this is equivalent to "-b swc" in cli
    "typeCheck": true,
    "deleteOutDir": false,
    "tsConfigPath": "apps/api/tsconfig.app.json"
  }
}

This is what you'll get.

This is due to SWC doesn't have a built-in modules resolution system.
It only builds root project of your repository.

Here come a Webpack

Since webpack has module resolution, it's going to do job for us.

// nest-cli.json
{
  "compilerOptions": {
    "builder": "webpack",
    "deleteOutDir": false,
    "tsConfigPath": "apps/api/tsconfig.app.json"
  }
}

SWC >

Webpack >

Of course, I configured a swc-loader in webpack.
and I double checked swc configuration was imported to webpack.

I'm not sure whatw as the problem. but with webpack, swc performance goes down.

And One more thing.

Webpack bundles your project files into a one big chunk.

If you're using TypeORM or MikroORM, You'd probably imports your entities like this.
This will break your app.

{
entities: ['dist/**/*.entity.js', 'libs/**/*.entity.js'],
entitiesTs: ['libs/**/*.entity.ts']
}

There is a way to not to bundle your files by configuring entry and output of webpack.config.
But, I won't recommend.

My Conclusion

• Using SWC in standard mode: go for it.
• Using SWC in monorepo mode: Don't. unless you can make your own custom scripts that can manage all the problems

Ref

• Nest.js 10 announcement
• Nest.js Monorepo mode
• Nest.js SWC configuration
• SWC monorepo issue