How to install a Node.js dependency

Node.js projects rely on npm packages for runtime libraries, build tools, and test utilities that live outside the project source. Adding a dependency with npm records the package in the project manifest so teammates and deployment systems can install the same requirement.

The npm install package-name command writes runtime packages to dependencies by default and updates package-lock.json when the project uses a lockfile. Use --save-dev for packages that only support local development, testing, linting, or builds.

Run the install from the project root that contains package.json, and review both package.json and package-lock.json before committing the dependency change. Replace the package name in the command with the library or tool the project needs.

1. Confirm npm is reading the expected project.

   $ npm pkg get name
   "demo-app"

   If npm reports that no package.json exists, open the correct project root or initialize the project first.
   Related: How to create a Node.js project with npm

2. Install the runtime dependency.

   $ npm install lodash
   
   added 1 package, and audited 2 packages in 558ms
   
   found 0 vulnerabilities

   Use --save-dev instead of the default runtime save for test runners, linters, build tools, and other development-only packages.

3. Check the saved dependency range in package.json.

   $ npm pkg get dependencies.lodash
   "^4.18.1"

   Use package@version when the project needs a specific release instead of the registry version selected by npm.

4. Check the lockfile entry.

   $ npm ls lodash --package-lock-only --depth=0
   demo-app@1.0.0 /path/demo-app
   `-- lodash@4.18.1

   --package-lock-only makes npm ls read package-lock.json instead of the installed node_modules tree.

5. Run a small import check.

   $ node -p 'require("lodash").kebabCase("Hello Node")'
   hello-node