Learn TypeScript 3 by Building Web Applications

Barrels

Barrels are a technique used to roll up exports from different modules into a single one, usually called index.ts, to simplify the imports. Barrels thus simply combine the exports of one or more other modules. By making use of the re-export functionality, you can actually create barrels.

For example, if you create a library, then it is useful to expose a single module exposing the public API to the outside world. As a consumer, barrels are useful because they let you concentrate on what you want to use and not on where symbols are located.

Here's an example of a barrel in the Angular framework: https://github.com/angular/angular/blob/master/packages/core/src/core.ts. This barrel is re-exported by https://github.com/angular/angular/blob/master/packages/core/public_api.ts ...