What is npx?

You may have heard of npm, but what about npx?

What is npx

npx is a executable that is bundled with npm@5.2.0 and above.

It makes running binaries from packages installed in your node projects much simpler!

To try npx out, just type npx {binaryName}. npx will start by checking your project’s local node_modules/.bin folder for the specified binaryName, and if it doesn’t find it there, it will move to your global installs.

If the binary isn’t found on your machine anywhere, it will install the latest version in a one off install, use it, then throw the install away! This way you don’t have to worry about polluting your global scopes with packages that you use once in a blue moon (like create-react-app for example).

Similar to one off scripts above, you can point npx to a remote javascript file via the url, and npx will download it and execute it for you.

For example:

npx https://gist.github.com/bambielli/8d7cb891423def24e643ac5be174bd03

should log the secret is: npx rox to your console

Always be careful when executing remote files that you do not own… be sure to read through them to make sure there isn’t any malicious code in there.

Use case for npx

This week at work I was using the sequelize-cli package to automate the execution of migrations and seed data for a hackathon project.

The binary was installed locally to my project under node_modules/.bin/sequelize, and the readme for sequelize-cli instructed to execute the binary by typing that full path before each command.

My first instinct was to turn this into an npm script, which I did:

// package.json

{
  //...
  "scripts": {
    "db:migrate" 'node_modules/.bin/sequelize db:migrate'
  }
}

I could run this script by typing npm run db:migrate, which is already pretty easy.

npx made life even easier, though: when I wanted to seed my database, I just ran npx sequelize db:seed from my command line, without needing to create a new npm script for seeding. Easy as that! No more typing the full node_modules path to your project binaries, or bloating your package.json with npm scripts that are shortcuts for project binaries.