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node.jsnpmyarnpkg

Pass arguments to “node” executable when running “yarn run”

node can be started with various options. Especially interesting is the --inspect flag:

node --inspect node_modules/.bin/jest some.spec.js

Is it possible to pass the --inspect flag somehow to yarn run? For example:

yarn run test --inspect some.spec.js

There is a similar question for npm run, where it seems to be not possible.

Solution

  • In general, yarn run ... does not support passing arbitrary arguments to NodeJS. However, the --inspect flag is an exception depending on your version of Yarn.

    As of March 2022, recent versions of Yarn support both --inspect and --inspect-brk arguments for the yarn run command. The answer to your questions is now "yes", and the following will work:

    yarn run --inspect some.spec.js

    For older versions of Yarn (or even NPM), there are a couple of options.

    First, you can use the NODE_OPTIONS environment variable to pass arguments to NodeJS. For example,

    export NODE_OPTIONS="--inspect"
yarn run test some.spec.js

    then in the package.json, you can define a script to take advantage of this:

    "scripts": {
  "test": "jest",
  "test:inspect": "NODE_OPTIONS='--inspect' yarn run test"
}

    Second, as you mentioned, you can use NodeJS directly,

    node --inspect ./node_modules/jest-cli/bin/jest.js some.spec.js

    For older versions of Yarn, those may be your only two options. However, both options work for both NPM and Yarn.