5 advanced npm package.json config tips

Originally published on davidwells.io

Node, npm, and package.json are super awesome.

Together they give devs a rich dev environment & build system out of the box.

Over my years as a node dev, I've gathered some advanced patterns for making npm scripts & package.json even more awesome, so I thought I'd share.

Hope these help ya. Also, leave a comment below if you have!

1. Using NPM script pre & post lifecycle

npm has built in lifecycle methods for your package scripts. When you use pre and post with commands, they will run before and after the given script.

An Example

{
  "name": "npm-lifecycle-example",
  "scripts": {
    "prefoo": "echo prefoo",
    "foo": "echo foo",
    "postfoo": "echo postfoo"
  }
}

Running npm run foo will run these three commands in order

1. prefoo,
2. foo,
3. then postfoo

Will result in:

echo prefoo
echo foo
echo postfoo

Use this for prebuild and postbuild (and whatever else 🌈). This is very handy for baking in deploy processes & chaining npm commands together.

2. Passing an argument into a command

You can dynamically pass values into an npm script.

To do this, you need to use the $npm_config_{key} value in your command.

Example:

{
  "name": "passing-flags-into-command",
  "scripts": {
    "pass-arg": "node scripts/lol.js --name=$npm_config_name",
  }
}

Then use it:

npm run pass-arg --name woot

In this example we are running lol.js with the arg.

const argv = require('minimist')(process.argv.slice(2));
console.log(argv.name);
// woot

This is super handy for makeshift CLI tools within your projects.

3. Using values from package.json config key

To avoid repeating configuration in a bunch of different scripts, You can reference values from the package.json file config field.

{
  "config": {
    "ENDPOINT": "my-value"
  },
  "scripts": {
    "set-env": "REACT_APP_ENDPOINT=$npm_package_config_ENDPOINT react-scripts start"
  }
}

This is handy for certain occasions

4. Using cross-env for cross platform scripts

The setting environment variables in a script is pretty easy, however they aren't cross platform compatible (cough cough windows)

The cross-env pkg from npm allows you sets ENV vars for command to use so anyone running your scripts will be happy.

Example:

{
  "name": "using-cross-env",
  "scripts": {
    "cross-env": "cross-env NODE_ENV=prod OTHERFLAG=xyz webpack --config webpack.js",
  }
}

This will set NODE_ENV=prod and OTHERFLAG=xyz to process.env variables for webpack to use (for example).

Props to kentcdodds for making this gem.

5. Passing arguments to other npm commands

Sometimes we need to pass additional arguments to an existing npm script.

Rather than altering the existing script every time we want the arg, or duplicating the script over and over, we can leverage the -- separator.

Example json

{
  "name": "passing-flags-example",
  "scripts": {
    "my-script": "esw src/components",
    "pass-flags-to-other-script": "npm run my-script -- --watch",
  }
}

This example below will pass the --watch flag to the my-script command

npm run pass-flags-to-other-script

Will run:

esw src/components --watch

This is super handy for setting up test scripts with a normal mode and a watch mode.

Putting it all together

Here is are all the methods combined into a MEGA json.

{
  "name": "advanced-package-json",
  "version": "0.1.0",
  "private": true,
  "config": {
    "SESSION_ENDPOINT": "my-value"
  },
  "dependencies": {
    "react": "^15.6.1",
  },
  "scripts": {
    "pass-arg": "node scripts/lol.js --name=$npm_config_name",
    "set-env": "REACT_APP_ENDPOINT=$npm_package_config_ENDPOINT react-scripts start",
    "cross-env": "cross-env NODE_ENV=prod OTHERFLAG=xyz webpack --config webpack.js",
    "my-script": "esw src/components",
    "pass-flags-to-other-script": "npm run my-script -- --watch",
  },
  "devDependencies": {
    "react-scripts": "^1.1.4",
    "cross-env": "^1.1.4"
  }
}

Do you know any other package.json tips?

Let me know in the comments below.

Go forth and

npm init