astTransformers.md

title
AST transformers option

ts-jest by default does hoisting for a few jest methods via a TypeScript AST transformer. One can also create custom TypeScript AST transformers and provide them to ts-jest to include into compilation process.

The option is astTransformers and it allows ones to specify which 3 types of TypeScript AST transformers to use with ts-jest:

• before means your transformers get run before TS ones, which means your transformers will get raw TS syntax instead of transpiled syntax (e.g import instead of require or define ).
• after means your transformers get run after TS ones, which gets transpiled syntax.
• afterDeclarations means your transformers get run during d.ts generation phase, allowing you to transform output type declarations.

Examples

// jest.config.js
module.exports = {
  // [...]
  globals: {
    'ts-jest': {
      astTransformers: {
        before: ['my-custom-transformer'],
      },
    }
  }
};

// OR package.json
{
  // [...]
  "jest": {
    "globals": {
      "ts-jest": {
        astTransformers: {
          "before": ["my-custom-transformer"]
        }
      }
    }
  }
}

Writing custom TypeScript AST transformers

To write a custom TypeScript AST transformers, one can take a look at the one that ts-jest is using.