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SWC

Warning SWC isn't compatible with NestJS CLI plugins. If you're using a plugin, you should stick to tsc or webpack (nest build and nest start).

SWC (Speedy Web Compiler) is an extensible Rust-based platform that can be used for both compilation and bundling.

Hint SWC is 20x faster than Babel on a single thread and 70x faster on four cores.

Installation#

To get started, first install a few packages:

$ npm i --save-dev @swc/cli @swc/core nodemon

Once the installation process is complete, let's create a new .swcrc file in the root directory of your application:

{
  "$schema": "https://json.schemastore.org/swcrc",
  "sourceMaps": true,
  "module": {
    "type": "commonjs"
  },
  "jsc": {
    "target": "es2017",
    "parser": {
      "syntax": "typescript",
      "decorators": true,
      "dynamicImport": true
    },
    "transform": {
      "legacyDecorator": true,
      "decoratorMetadata": true
    },
    "keepClassNames": true,
    "baseUrl": "./"
  },
  "minify": false
}

Scripts#

To make the development process easier, let's add a few scripts to the package.json file:

{
  "scripts": {
    "build:swc": "npx swc --out-dir dist -w src",
    "start:swc": "nodemon dist/main"
  }
}

Hint Both scripts are dedicated for development purposes only.

Now, open up the terminal and run the follwoing command:

$ npm run build:swc

In another terminal window, run the following command:

$ npm run start:swc

Every time you make a change to your application, the build:swc script will recompile your application and the start:swc script will restart the application.

Common pitfalls#

If you use TypeORM/MikroORM or any other ORM in your application, you may stumble upon circular import issues. SWC doesn't handle circular imports well, so you should use the following workaround:

@Entity()
export class User {
  @OneToOne(() => Profile, (profile) => profile.user)
  profile: Relation<Profile>; // <--- see "Relation<>" type here instead of just "Profile"
}

HintRelation type is exported from the typeorm package.

Doing this prevents the type of the property from being saved in the transpiled code in the property metadata, preventing circular dependency issues.

If your ORM does not provide a similar workaround, you can define the wrapper type yourself:

/**
 * Wrapper type used to circumvent ESM modules circular dependency issue
 * caused by reflection metadata saving the type of the property.
 */
export type WrapperType<T> = T; // WrapperType === Relation

Vitest

Vitest is a fast and lightweight test runner designed to work with Vite. It provides a modern, fast, and easy-to-use testing solution that can be integrated with NestJS projects.

Installation#

To get started, first install the required packages:

$ npm i --save-dev vitest unplugin-swc @swc/core @vitest/coverage-c8

Configuration#

Create a vitest.config.ts file in the root directory of your application with the following content:

import swc from 'unplugin-swc';
import { defineConfig } from 'vitest/config';

export default defineConfig({
  test: {
    globals: true,
    root: './',
  },
  plugins: [
    // This is required to build the test files with SWC
    swc.vite({
      // Explicitly set the module type to avoid inheriting this value from a `.swcrc` config file
      module: { type: 'es6' },
    }),
  ],
});

This configuration file sets up the Vitest environment, root directory, and SWC plugin. You should also create a separate configuration file for e2e tests, with an additional include field that specifies the test path regex:

import swc from 'unplugin-swc';
import { defineConfig } from 'vitest/config';

export default defineConfig({
  test: {
    include: ['**/*.e2e-spec.ts'],
    globals: true,
    root: './',
  },
  plugins: [swc.vite()],
});

Additionally, you can set the alias options to support TypeScript paths in your tests:

import swc from 'unplugin-swc';
import { defineConfig } from 'vitest/config';

export default defineConfig({
  test: {
    include: ['**/*.e2e-spec.ts'],
    globals: true,
    alias: {
      '@src': './src',
      '@test': './test',
    },
    root: './',
  },
  resolve: {
    alias: {
      '@src': './src',
      '@test': './test',
    },
  },
  plugins: [swc.vite()],
});

Update imports in E2E tests#

Change any E2E test imports using import * as request from 'supertest' to import request from 'supertest'. This is necessary because Vitest, when bundled with Vite, expects a default import for supertest. Using a namespace import may cause issues in this specific setup.

Lastly, update the test scripts in your package.json file to the following:

{
  "scripts": {
    "test": "vitest run",
    "test:watch": "vitest",
    "test:cov": "vitest run --coverage",
    "test:debug": "vitest --inspect-brk --inspect --logHeapUsage --threads=false",
    "test:e2e": "vitest run --config ./vitest.config.e2e.ts"
  }
}

These scripts configure Vitest for running tests, watching for changes, generating code coverage reports, and debugging. The test:e2e script is specifically for running E2E tests with a custom configuration file.

With this setup, you can now enjoy the benefits of using Vitest in your NestJS project, including faster test execution and a more modern testing experience.

Hint You can check out a working example in this repository