npm

You might say

AI told me to install dependencies, and one command downloaded a ton of stuff. What's going on?

Install JavaScript packages and run project scriptsnpm is a package manager and command runner for JavaScript projects. package.json records dependencies and named scripts, while the lockfile keeps installed versions reproducible. Install packages intentionally and review scripts before running code from an unfamiliar project.

Know first

Terminal

package.json · Manifest "react": "^19.0.0" "vite": "^6.0.0" "scripts": dev / build

npm
install
→

node_modules · Dependency directory 📦 react 📦 vite 📦…42 packages in total

When to use it

Install declared dependencies
Add a library to a project
Run scripts such as dev, test, and build
Keep dependency versions reproducible with a lockfile

When NOT to use it

Commit the node_modules directory
Delete the lockfile whenever versions conflict
Install a package before checking whether the platform already provides the feature
Run an unfamiliar package script without reading it

Anatomy

{ "name": "my-first-page", "dependencies": { "react": "^19.0.0" }, "scripts": { "dev": "vite", "build": "vite build" } }

The name and version of the project, used when publishing and sharing

Which packages and versions are installed; install and move the goods accordingly.

npm run dev runs the command written here

Variants

install

npm install

Install new packages, or rebuild node_modules

run

npm run dev

Execute shortcut commands in scripts

uninstall

npm uninstall lodash

The bag is no longer needed, so cross it off the list.

lockfile

package-lock.json

Team unified version, don’t change it manually

Typical use cases

Project setup

package.json

        {

          "name": "my-first-page",

          "dependencies": { "react": "^19.0.0" },

          "scripts": { "dev": "vite", "build": "vite build" }

        }

Add dependency

zsh — my-first-page

$ npm install ⸨████████░░⸩ reify: react added 42 packages in 6s Dependencies will be installed to node_modules according to package.json and lock files

Development server

my-first-page

📁 node_modules380 MB · ⚠ Automatically generated, do not move

📄 package.jsonEvents

📄 .gitignoreIt says node_modules and .env

Production build

zsh — my-first-page

$ npm run dev > my-first-page@0.1.0 dev ✓ Ready in 1.2s → http://localhost:3000 Shortcut commands in scripts, one for each string