ESM Support

References

• Configuration
• Resolve .mjs/.mts extensions

---

Configuration

To use ts-jest with ESM support:

• Check ESM Jest documentation.
• Ensure that tsconfig has module with value for ESM, e.g. ES2022/ESNext etc...

Example:

// tsconfig.spec.json
{
  "compilerOptions": {
    "module": "ESNext", // or ES2022
    "target": "ESNext",
    "esModuleInterop": true
  }
}

• Configure your Jest configuration use one of the utility functions

Example:

// jest.config.mts
import { createDefaultEsmPreset, type JestConfigWithTsJest } from 'ts-jest'

const presetConfig = createDefaultEsmPreset({
  //...options
})

const jestConfig: JestConfigWithTsJest = {
  ...presetConfig,
}

export default jestConfig

Resolve .mjs/.mts extensions

To work with .mts extension, besides the requirement to run Jest and ts-jest in ESM mode, there are a few extra requirements to be met:

• package.json should contain "type": "module"
• A custom Jest resolver to resolve .mjs extension, for example:

TypeScript CJS

import type { SyncResolver } from 'jest-resolve'

const mjsResolver: SyncResolver = (path, options) => {
  const mjsExtRegex = /\.mjs$/i
  const resolver = options.defaultResolver
  if (mjsExtRegex.test(path)) {
    try {
      return resolver(path.replace(mjsExtRegex, '.mts'), options)
    } catch {
      // use default resolver
    }
  }

  return resolver(path, options)
}

export = mjsResolver

TypeScript ESM

import type { SyncResolver } from 'jest-resolve'

const mjsResolver: SyncResolver = (path, options) => {
  const mjsExtRegex = /\.mjs$/i
  const resolver = options.defaultResolver
  if (mjsExtRegex.test(path)) {
    try {
      return resolver(path.replace(mjsExtRegex, '.mts'), options)
    } catch {
      // use default resolver
    }
  }

  return resolver(path, options)
}

export default mjsResolver