#@swc/jest

To make your Jest tests run faster, you can swap out the default JavaScript-based runner (ts-jest) for a drop-in Rust replacement using SWC.

#Installation

pnpm i -D jest @swc/core @swc/jest

npm i -D jest @swc/core @swc/jest

yarn add -D jest @swc/core @swc/jest

#Usage

Inside jest.config.js, configure Jest to use SWC:

module.exports = {
  transform: {
    '^.+\\.(t|j)sx?$': '@swc/jest',
  },
}

It will load the SWC configuration from .swcrc by default. You also can customize it:

const fs = require('fs')

const config = JSON.parse(fs.readFileSync(`${__dirname}/.swcrc`, 'utf-8'))

module.exports = {
  transform: {
    '^.+\\.(t|j)sx?$': ['@swc/jest', { ...config, /* custom configuration in Jest */ }],
  },
}

#Q & A

#Q: Jest uses CommonJS by default. But I want to use ESM

A: Setup Jest following this Guide.

For JavaScript, edit package.json as follows:

{
  // ...
  "type": "module"
}

For TypeScript, edit jest.config.js as follows:

module.exports = {
  // ...
  extensionsToTreatAsEsm: ['.ts', '.tsx'],
}

Run test with --experimental-vm-modules:

cross-env NODE_OPTIONS=--experimental-vm-modules jest

# or
node --experimental-vm-modules ./node_modules/jest/bin/jest.js

#Q: What ECMAScript target is set by jsc.target?

A: By default, the version supported by your Node runtime.

You can customize this by setting an explicit version in jest.config.js:

module.exports = {
    transform: {
        "^.+\\.(t|j)sx?$": [
            "@swc/jest",
            {
                jsc: {
                    target: "es2021",
                },
            },
        ],
    },
}