npm scripts — define and run custom commands

Quick Answer

# Run a script
npm run build
npm run dev
npm run test

# Shorthand for built-in scripts (no "run" needed)
npm start
npm test

Usage

Automate project tasks (build, test, lint, deploy) using npm scripts defined in package.json.

Other causes & fixes

Defining scripts in package.json

{
  "scripts": {
    "dev":   "vite",
    "build": "tsc && vite build",
    "test":  "vitest run",
    "lint":  "eslint src --ext ts,tsx"
  }
}

Chaining commands

{
  "scripts": {
    // Run sequentially (stop on failure)
    "build": "tsc && vite build",

    // Run in parallel
    "dev":   "tsc -w & vite",

    // Cross-platform parallel (use npm-run-all)
    "dev2":  "run-p tsc:watch vite:serve"
  }
}

Passing arguments to a script

npm run test -- --watch
# Everything after -- is forwarded to the script

Pre and post hooks

{
  "scripts": {
    "prebuild":  "rm -rf dist",
    "build":     "vite build",
    "postbuild": "gzip dist/assets/*.js"
  }
}
# prebuild runs before build, postbuild runs after

Set environment variables cross-platform

# Install cross-env
npm install --save-dev cross-env

{
  "scripts": {
    "build:prod": "cross-env NODE_ENV=production vite build"
  }
}