Isolated Modules option

By default ts-jest uses TypeScript compiler in the context of a project (yours), with full type-checking and features. But it can also be used to compile each file separately, what TypeScript calls an ‘isolated module’. That’s what the isolatedModules option (which defaults to false) does.

You’ll lose type-checking ability and some features such as const enum, but in the case you plan on using Jest with the cache disabled (jest --no-cache), your tests will then run much faster.

Here is how to disable type-checking and compile each file as an isolated module:

Example

// jest.config.js
module.exports = {
  // [...]
  globals: {
    'ts-jest': {
      isolatedModules: true
    }
  }
};

// OR package.json
{
  // [...]
  "jest": {
    "globals": {
      "ts-jest": {
        "isolatedModules": false
      }
    }
  }
}