How does npm run build work with npm pack?

Question

I'm working on a project that requires using the npm pack command. Is running build on the library/package required before creating the installable tar file? Or can I just pack and then install it into the app?

Answer 1

Yes, but for totally different reasons.

• npm run build can do anything: it just executes the value for build inside the scripts object in your package.json, for example on an Angular project it'll look like this,

  "scripts": {
    "ng": "ng",
    "start": "ng serve",
    "build": "ng build",
    "test": "ng test",
    "lint": "ng lint",
    "e2e": "ng e2e"
  },  
  

• npm pack basically "create a tarball from a package", but here is the deal: the "package" that it creates a tarball from has to exist. So, in order to create the "package" that npm pack targets in ./dist you frequently have to run npm build. This is because many JavaScript projects are written in TypeScript (in which case "build" usually runs npx tsc) or use a build system that will transpile their code to produce JavaScript (like babel). If your project is very rudimentary, there is a good chance you won't have to "build anything": you can see this if you create an empty directory and run npm init, but seldom are useful packages created this way.

The result of npm pack is a .tgz file. This is basically a compressed copy of a target directory. You can install this with npm i ./file.tgz. On the consuming machine that you wish to install the package on, you do not have to build anything. Building is what you do as a developer and a package maintainer. For example, you build TypeScript producing JavaScript. The consumer just downloads the result and installs the dependencies. It doesn't even have to know that you write your code with TypeScript (or better, Rust.)