@yarnpkg/fslib

A TypeScript library abstracting the Node filesystem APIs. We use it for three main reasons:

Type-safe paths

Our library has two path types, NativePath and PortablePath. Most interfaces only accept the later, and instances of the former need to be transformed back and forth using our type-safe utilities before being usable.

Custom filesystems

The FSLib implements various transparent filesystem layers for a variety of purposes. For instance we use it in Yarn in order to abstract away the zip archive manipulation logic, which is implemented in ZipFS and exposed through a Node-like interface (called FakeFS).

All FakeFS implementations can be transparently layered on top of the builtin Node fs module, and that's for instance how we can add support for in-zip package loading without you having to care about the exact package format.

Promisified API

All methods from the FakeFS interface are promisified by default (and suffixed for greater clarity, for instance we offer both readFileSync and readFilePromise).