This is an example package that can be used to test Yarn.

It has the common default fields in its package.json, along with production and development dependencies as well that are specific to the package we have created.

The package.json

Default Package Fields

yarn init produces a default package.json similar to:

{
  "name": "example-yarn-package",
  "version": "1.0.0",
  "description": "An example package to demonstrate Yarn",
  "main": "index.js",
  "repository": {
    "url": "github.com/yarnpkg/example-yarn-package",
    "type": "git"
  },
  "author": "Yarn Contributors",
  "license": "BSD-2-Clause",
}

Custom Package Fields

You can add custom fields to your package.json as well. In our case, we have added 4 custom fields.

The scripts field are for any special scripts that you want to use when running yarn. For example, here we add a script called test that calls the Jest test runner because we added Jest tests to our Yarn package.

"scripts": {
  "test": "jest"
},

The dependencies field lists the other packages that this package is dependent upon. Our example package is dependent on Lodash since we use its multiply function.

"dependencies": {
  "lodash": "^4.16.2"
},

The devDependencies field lists the other packages that this package is dependent upon during development. Our example package is dependent on Jest since we created some Jest-enabled tests for our package.

"devDependencies": {
  "jest-cli": "15.1.1"
},

The jest field is a custom field specific to the Jest package we included as a dev dependency. In this case, we are testing in a node environment at the command-line.

"jest": {
  "testEnvironment": "node"
}

It is important to note that Lodash and Jest are not required for Yarn. They are just examples of what can be used when you are creating the code for your Yarn package.

Development

$ yarn install
$ yarn run test

Production

$ yarn install --production