export default {
  preset: 'ts-jest/presets/default-esm',
  testEnvironment: 'node',
  extensionsToTreatAsEsm: ['.ts'],
  transform: {
    '^.+\\\\.tsx?$': ['ts-jest', { useESM: true }]
  },
  moduleNameMapper: {
    '^(\\\\.{1,2}/.*)\\\\.js$': '$1'
  }
};

The 4 Critical Requirements (Short Notes)

1. preset: 'ts-jest/presets/default-esm'

• Enables ESM mode inside Jest.

• Makes Jest understand import & export.

• Without this → Jest treats everything as CommonJS → errors like:

  SyntaxError: Cannot use import statement outside a module
  

2. extensionsToTreatAsEsm: ['.ts']

• Tells Jest: .ts files are ESM, not CommonJS.
• Needed because Jest assumes .ts = CommonJS by default.

Without this → Jest rewrites imports to require() → breaks.

3. transform: { useESM: true }

• Directs ts-jest to compile TypeScript into ESM output.
• Without this, ts-jest compiles to CommonJS, even in ESM mode.

Without this → TypeScript compiles to:

const x = require('./file');

→ breaks ESM imports.

4. moduleNameMapper: { '^(\\\\.{1,2}/.*)\\\\.js$': '$1' }