compilerHost.md

title	Compiler Host option

By default ts-jest uses TypeScript LanguageService API in the context of a project (yours), with full type-checking and features. But TypeScript Program can also be used to achieve the same behavior as LanguageService. That's what the compilerHost option (which defaults to false) does.

There are 2 types of TypeScript Program, one is Incremental Program which is only available from TypeScript 3.4 and the other one is normal Program.

By default ts-jest uses Incremental Program if compilerHost is enabled. The priority of using TypeScript APIs in ts-jest as below:

• Default TypeScript API is LanguageService.
• compilerHost is enabled:
  • incremental is enabled (default): use TypeScript Incremental Program.
  • incremental is disabled: use TypeScript Program.
• isolatedModules is enabled, use TypeScript transpile modules.

Here is how to enable ts-jest to compile using TypeScript Program

Example

// jest.config.js
module.exports = {
  // [...]
  globals: {
    'ts-jest': {
      compilerHost: true,
      incremental: false,
    }
  }
};

// OR package.json
{
  // [...]
  "jest": {
    "globals": {
      "ts-jest": {
        "compilerHost": true,
        "incremental": false
      }
    }
  }
}

Here is how to enable ts-jest to compile using TypeScript IncrementalProgram

Example

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

// OR package.json
{
  // [...]
  "jest": {
    "globals": {
      "ts-jest": {
        "compilerHost": true
      }
    }
  }
}