Is a package.json file missing dependencies?

Curious about the meaning of peerDependencies, I examined the contents of this package.json file. It relates to a library project that is distributed elsewhere.

{
    "name": "...",
    "version": "...",
    "description": "...",
    "author": "...",
    "license": "Unlicense",
    "main": "dist/index.js",
    "typings": "dist/index.d.ts",
    "scripts": {
      "build": "typings install && tsc --outDir dist/"
    },
    "peerDependencies": {
        "@angular/core": "^2.0.0",   <<<<<<<<
        "@angular/http": "^2.0.0",   <<<<<<<<
        "@angular/common": "^2.0.0",   <<<<<<<<
        "@angular/compiler": "^2.0.0",   <<<<<<<<
        "core-js": "^2.4.0",   <<<<<<<<
        "reflect-metadata": "^0.1.3",   <<<<<<<<
        "rxjs": "5.0.0-beta.12",   <<<<<<<<
        "zone.js": "^0.6.17"   <<<<<<<<
      },
      "devDependencies": {
        "@angular/core": "^2.0.0",   <<<<<<<<
        "@angular/http": "^2.0.0",   <<<<<<<<
        "@angular/common": "^2.0.0",   <<<<<<<<
        "@angular/compiler": "^2.0.0",
        "@angular/platform-browser": "^2.0.0",   <<<<<<<<
        "core-js": "^2.4.0",   <<<<<<<<
        "reflect-metadata": "^0.1.3",   <<<<<<<<
        "rxjs": "5.0.0-beta.12",   <<<<<<<<
        "zone.js": "^0.6.17",   <<<<<<<<
        "typescript": "^2.0.0",
        "typings": "^1.3.2"
      }
}
  1. Why is the same package listed in both devDependencies and peerDependencies?
  2. Why isn't dependencies used here?
typescriptnpm

Answer №1

Starting from npm 3, peerDependencies are no longer automatically fetched when installing a package. Instead, npm will now issue a warning if a dependency is missing.

The rationale behind organizing a package.json in this way could be:

  • Developers working on this package are required to install the dependencies listed under devDependencies.

  • Users utilizing this package may not need to download the dependencies if they already exist in their project. However, in case they do not have them installed yet, the inclusion of peerDependencies ensures that they receive a warning during installation (which they would then have to resolve manually).

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