Usage with TypeScript

Since Japa does not have any CLI, you do not have to rely on us to add explicit support for TypeScript. Instead, you can use your existing tooling to run Japa tests within a TypeScript project.

In this guide, we will set up ts-node to execute Japa tests for both ESM and CommonJS projects.

CommonJS projects

Install the ts-node package from the npm registry.

npm i -D ts-node

Next, let's use ts-node and hook into the require lifecycle of Node.js to run the bin/test.ts file.

node -r ts-node/register bin/test.ts

You can also add the above command as a script inside the package.json file.

{
  "scripts": {
    "test": "node -r ts-node/register bin/test.ts"
  }
}

By default, ts-node will perform type-checking every time you run tests. However, type-checking is usually slow, and you can turn it off by adding the following configuration block inside the tsconfig.json file.

"ts-node": {
  "transpileOnly": true
}

ESM projects

Install the ts-node package from the npm registry.

npm i -D ts-node

Next, let's use ts-node as an ESM loader to pre-compile TypeScript source files to JavaScript during imports.

node --loader=ts-node/esm bin/test.ts

You can also add the above command as a script inside the package.json file.

{
  "scripts": {
    "test": "node --loader=ts-node/esm bin/test.ts"
  }
}

By default, ts-node will perform type-checking every time you run tests. However, type-checking is usually slow, and you can turn it off by adding the following configuration block inside the tsconfig.json file.

"ts-node": {
  "transpileOnly": true
}

Using SWC

SWC is a Rust-based TypeScript compiler. ts-node has first-class support for using SWC in place of the TypeScript official compiler. Let's open the tsconfig.json file and paste the following configuration inside.

"ts-node": {
  "swc": true
}