Typescript

Typescript files

Implementation files — .ts

• Contain types and executable code

Declaration files — .d.ts

• contain only type information
• lib.[something].d.ts are declaration files for built-in types

DefinitelyTyped/@types

Centralised repo storing declaration files. Definitions on DefinitelyTyped are automatically published to npm under the @types scope.

@types in dependencies vs devDependencies

If you use the type in implementation files, import with devDependencies

If you use the type in declaration files, import with dependencies