Working with Third-Party JavaScript

Most npm packages are written in plain JavaScript, with no types of their own — the @types packages (from the community-run DefinitelyTyped project) provide type information for them separately.

npm install lodash
npm install --save-dev @types/lodash

Many newer packages ship their own types built in (no separate @types package needed) — TypeScript picks those up automatically. If no types exist anywhere for a package, importing it falls back to any, unless you write your own minimal declaration file (Level 3).