NPM Failsafe

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The npm-failsafe lets you execute a sequence of NPM scripts and return the correct exit code should any of them fail.

Usage

Installation:

npm install --save-dev npm-failsafe

In your project:

You should use this to run only scripts which are defined in your package.json file. Ideally, you should also provide all args for these scripts upfront, due to the order in which scripts/args are interpreted:

Each script will be executed with npm run.

Best practice use case

{
    "scripts": {
        "test": "jest",
        "test:coverage": "npm run test -- --coverage",
        "lint": "eslint src/*",
        "start": "pm2 start server.js --port=3000",
        "ci": "failsafe start lint test:coverage"
    }
}

In the above example, you can see that args for each script on which failsafe will run have been provided upfront.

Motivation

Assume a package.json with the following scripts defined:

"scripts": {
    "preintegration": "bin/start_the_server.sh",
    "integration": "bin/run_some_tests_that_require_the_server.sh",
    "cleanup": "bin/shutdown_the_server.sh"
}

In this example, we want to execute the integration script. The script runs some integration tests against some server, which means that we need to start the server up before the tests and shut it down afterwards.

The server itself is started in the preintegration phase (check out the node docs to learn more about the pre- and post- commands).

The question is: how do we shut it down?

We could add the following test script to our package.json: "test": "integration && cleanup".

The problem with this is that because of how the && operator works, the cleanup script will only get executed when the integration script succeeds. This is no good because we need to shut down the server even if the integration tests fail.

We could try to use the || operator instead, which executes the second script no matter the result of the first one: "test": "integration || cleanup". However, the problem with this approach is that the exit code of the "integration || cleanup" combo will always take the value of 0, incorrectly indicating that the test script has succeeded. This could for example cause a continuous integration server to publish your project even if the tests have failed...

Enter npm-failsafe!

With npm-failsafe you can execute a sequence of arbitrary NPM scripts and return the correct exit code should any of them fail:

"scripts": {
     "preintegration": "bin/start_the_server.sh",
     "integration": "bin/run_some_tests_that_require_the_server.sh",
     "cleanup": "bin/shutdown_the_server.sh",

     "test": "failsafe integration cleanup"
}

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Have feedback? Let me know on twitter: @JanMolak