What are npm scripts and lifecycle hooks?

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**npm scripts** are commands defined in `package.json`'s `scripts` field that you run with `npm run `. They standardize project tasks (start, build, test, lint) so the whole team and CI use the same commands. **Lifecycle hooks** are special scripts npm runs automatically at certain points. ## Defining and running scripts ```json { "scripts": { "start": "node server.js", "dev": "nodemon server.js", "build": "tsc && vite build", "test": "vitest", "lint": "eslint src", "format": "prettier --write ." } } ``` ```bash npm run dev # any script npm start # `start` and `test` have shortcuts (no "run" needed) npm test ``` Scripts can chain commands with `&&` (run sequentially, stop on failure) and have access to locally-installed binaries (in `node_modules/.bin`) without a path — so `"test": "vitest"` works even though vitest isn't global. ## Pre and post hooks (automatic) ```json { "scripts": { "prebuild": "rimraf dist", // runs AUTOMATICALLY before "build" "build": "tsc", "postbuild": "echo done" // runs AUTOMATICALLY after "build" } } ``` npm automatically runs `pre` before and `post` after any script ``. So `npm run build` runs `prebuild` → `build` → `postbuild` in order — handy for setup/cleanup steps. ## Built-in lifecycle hooks ```json { "scripts": { "postinstall": "node setup.js", // runs after `npm install` completes "prepare": "husky install" // runs after install (commonly sets up git hooks) } } ``` Hooks like `postinstall` and `prepare` run at defined moments of the install lifecycle — often used to set up git hooks (husky) or compile native dependencies. (Be cautious: `postinstall` scripts in dependencies are also a supply-chain security consideration.) ## Passing arguments and env vars ```bash npm run test -- --watch # pass args to the script after -- NODE_ENV=production npm start # set an env var for the run ``` ## Why npm scripts over a Makefile/global tools ```text ✓ Self-documenting — `package.json` shows all available tasks ✓ Cross-platform-ish, no global installs needed (uses local node_modules/.bin) ✓ Standard across the JS ecosystem — every dev knows `npm run` ``` ## Why it matters npm scripts are the standard task runner for Node/JS projects — they centralize and document how to start, build, test, and lint the app, ensuring everyone (and CI) runs identical commands. Understanding script composition, the automatic `pre`/`post` hooks (for setup/cleanup), and lifecycle hooks like `postinstall`/`prepare` lets you automate project workflows cleanly. They're the glue of project tooling and appear in essentially every Node repository.