How to run NPM scripts without issues when they don't exist

A while back I started consolidating all my release scripts and ran into an issue, that on the second look is quite obvious to solve, but I still wanted to share it with you.

You might run into situations, where you have scripts that are only relevant for certain builds or environments. For instance, in a Continuous Integration (CI) setup, you might have specific scripts for deployment, linting, or testing that do not apply to every build.

My first idea was to load package.json into a JSON object and then search for the script I want to run. If it exists, I would run it, otherwise, I would skip it. This approach works, but it’s not very elegant and requires a lot of boilerplate code.

Happily enough it turned out, that npm has a built-in option to handle this scenario. The --if-present flag alters the behavior of npm run-script (or npm run). Normally, if you try to execute a script that is not defined in your package.json file’s scripts section, npm exits with an error code. When --if-present is set to true, npm will not throw an error. Great.

If the script is present and it fails during execution, npm will still exit with an error. This ensures that while the script’s absence is tolerated, its failure is not, maintaining a level of strictness in your workflow.

1npm run lint --if-present

Important Note: It’s crucial to note that the --if-present value does not get exported to the environment for child processes. This means that the flag’s state won’t be automatically passed to scripts triggered by the initially executed script.