Using Jest with SWC, TypeScript, and ESM

jest-swc-typescript-esm.md

Using Jest with SWC, TypeScript, and ESM

Install dependencies

pnpm add -D jest @jest/globals @types/jest @swc/jest

Create jest.config.js file

/** @type {import('jest').Config} */
const config = {
  testMatch: [
    '<rootDir>/src/**/*.test.ts',
  ],
  moduleFileExtensions: [
    'js', 'ts',
  ],
  moduleNameMapper: {
    '^(\\.{1,2}/.*)\\.jsx?$': '$1',
  },
  transform: {
    '^.+\\.tsx?$': ['@swc/jest', {
      // Your SWC config here
    }],
  },
};

export default config;

Write your tests

import { describe, it, expect } from '@jest/globals';

import { greet } from './greet.js';


describe('encodeTlData()', () => {

  it('works', () => {

    expect(
      greet('John')
      
    ).toEqual('Hello John!');

  });

});

Notes

• SWC doesn't support tsconfig.json, therefore it's lacking from the configuration.

• Why not jest.config.ts? Jest requires ts-node to read config in TS format, however, the ts-node is no longer maintained and doesn't support various new features like multiple extends in tsconfig.json. We also like to keep our dependencies minimal.

• SWC is very fast but doesn't type-check! So make sure to check your types inside your IDE or using TypeScript compiler. Always check your types as part of CI/CD (before running tests)!

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