We'll get Hello true true Kundel Dominik instead because it will interpret -last and -first as boolean flags and set their value to true and will pass the rest of the arguments to the script as unparsed arguments resulting in echo "Hello $npm_config_first $npm_config_last" "Kundel" "Dominik" being called.īut even with the argument parser being fairly strict, this is a super powerful tool if you are planning to create a few simple scripts and don't want to have to deal with the argument parsing. The first one way just passes the arguments directly to your actual command. There are two different ways you can pass arguments to npm scripts. However, sometimes you want to be able to pass arguments to your scripts so that they can be more dynamic. So far we covered how to create scripts, which environment variables are set and how to call the scripts. There's a variety of different useful variables in here and I encourage you to check it out, especially if you are working on creating automation scripts.Ĭheck out my blog post If you want to learn more about environment variables in Node.js in generalt. You can get the git hash of the HEAD through npm_package_gitHead.The format runs along the lines of npm/6.10.0 node/v10.19.0 darwin 圆4 where darwin means macOS and 圆4 is the processor architecture You can get the npm version, node version and operating system through the npm_config_user_agent.In order to access values inside an array you use the index value prefixed with an _, like npm_package_keywords_0 to retrieve the first keyword. For example npm_package_dependencies_twilio will give you the version of twilio that is installed or npm_package_author_email would give you the email field of the author property. The accessing is done similar to accessing a property in JSON except that it's all using _ as separators. You can find every single entry of your package.json as an environment variable.Then run npm run check-env in your command-line and you should see a list of all the environment variables that npm has set for you. If you are curious of all the values that are passed to scripts in your project, add the following entry to your scripts: anything starting with npm_package_ is specific to your project.anything starting with npm_config_ is general npm configuration from your global npm config or from a project specific.When you run a command or script through npm run., your environment variables will automatically be augmented with a set of variables from npm.Īll environment variables are prefixed with npm_ and can be grouped into two types: The next thing was a pleasant surprise for me the first time I discovered it. You can read more about those lifecycle scripts in the npm docs. Where the difference between version and postversion is that postversion will be called after npm has committed the changes performed in preversion and version. An odd one here is version because it provides preversion, version and postversion. The same behavior also applies for built-in commands. downloading data before building your application.It's a great way to chain commands without convoluting your scripts. This works because npm will automatically detect if a script has other scripts named the same way but prefixed with pre or post and will execute those in the respective order. test is executed running the jest test runner.postbuild will be called running npm run test.build is executed running the TypeScript compiler.prebuild will be called executing the rimraf tool to delete the dist folder.If you now run npm run build the following things will automatically be triggered: įor example if our package.json looks like this: These can then be executed using npm run. The scripts field holds an object where you can specify various commands and scripts you want to expose. When we talk about "npm scripts" we are talking about entries in the scripts field of the package.json. Everything in this post has been tested with npm version 6.10. While a lot of these things should work in yarn, berry and pnpm as well, we'll focus on npm in this article. In this blog post we'll talk about the most useful and some hidden features.īefore we get started, make sure you have the latest version of npm installed. While you might have used this to set up your "build", "dev" or "start" script, there's a lot of things you can do with them. This is where "npm scripts" come into place. However, sometimes you still have the need for very custom configurations and scripts. The Node.js ecosystem is full with useful CLI tools and most of them offer configurations that let you tune them to do exactly what you want.
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