What is npx, and how do npm scripts work?

Answer:

npm scripts: Defined under scripts in package.json and run via npm run <name>:

"scripts": {
  "start": "node index.js",
  "dev": "nodemon src/index.js",
  "test": "jest",
  "lint": "eslint src",
  "build": "tsc"
}

• Run with npm run dev. start and test are special and also work as npm start / npm test.
• During a script, node_modules/.bin is added to PATH, so you can call locally-installed tools (jest, eslint, tsc) by name without a global install.
• Lifecycle hooks: a script named pre<name> runs before, and post<name> runs after (e.g., pretest runs before test).

npx: npx executes a package binary without a permanent global install:

npx create-react-app my-app   # download + run a scaffolder once
npx eslint .                  # run the locally installed eslint
npx cowsay hello              # try a tool without installing it

Resolution order: a matching binary in the local node_modules/.bin first, otherwise npx downloads the package to a temporary cache and runs it.

Why it matters:

• Avoids polluting the global namespace and version drift from globally installed CLIs.
• Ensures you run the project's pinned version of a tool rather than whatever is installed globally.