npm run and npx — running tools without installing them globally

Level: 101 · for anyone who has run npm test

Stub — an outline, not a lesson. There is no runnable example behind this page yet, so nothing on it has been through the check that backs every other claim in this library. The questions below are what the finished page has to answer.

One line: npm run puts node_modules/.bin first on PATH — the package's own and every parent folder's — so a script can call tsc by name; npx tsc outside a TypeScript project would fetch the package named tsc, a deprecated 2.0.4 release, which npx --no refuses.

Keywords: npm run, npx, node_modules/.bin, npm_lifecycle_event

What the finished page will answer

• Which folders does npm run put in front of PATH, and in what order?
• How does npm run build -- --watch pass --watch to the script, and what do npm_lifecycle_event and npm_package_name hold inside it?
• What does npx tsc --version print inside the repo, and what does npx --no tsc say in an empty folder?
• Where does npx keep a package it downloads, and what does --package=typescript change?
• Which script names run without run, such as npm test, and when do pretest and posttest run?

Examples it will need

• npm_scripts_path_sh.sh — the first PATH entries inside npm run for a package two folders deep
• npm_scripts_arguments_and_env_sh.sh — npm run passing arguments after --, and the npm_lifecycle_event and npm_package_name a script sees
• npx_inside_and_outside_a_project_sh.sh — npx --no tsc --version in the repo (7.0.2), then in an empty folder with a fresh cache: the refusal naming tsc@2.0.4

See also

• npm — where scripts and devDependencies are declared
• tsc and tsconfig.json — the tsc a script should find
• The built-in test runner — npm test running node --test
• process — the npm_ variables arrive in process.env
• Rust: Cargo subcommands worth knowing ↗ — subcommands in Cargo, the nearest thing to npm scripts

Sources to start from

• npm Docs — npm run ↗
• npm Docs — npx ↗
• npm Docs — scripts ↗