Overview

Backends in ZenFS are configuration-driven objects that instantiate storage implementations conforming to the internal API. Rather than directly handling file operations, the VFS routes all interactions through a backend, which creates and configures a FileSystem instance.

Configuration

Backends in ZenFS are designed to be configuration-driven. Each backend provides:

A name, used to identify the backend type.

A set of configuration options, defined via OptionsConfig<T>.

A create method, which returns an instance of FileSystem or a promise resolving to an instance of FileSystem.

An example

An example implementation of a backend might look something like this:

interface ExampleOptions {
	raw: RawExampleData; // e.g. `Storage` for a backend that works with `localStorage`
}

const Example = {
	name: 'ExampleStorage',
	options: {
		raw: { type: 'object', required: true },
	},
	async create({ raw }: ExampleOptions) {
		await raw.doSomethingAsync();
		return new ExampleFS(raw);
	},
} as const satisfies Backend<ExampleFS, ExampleOptions>;
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Why do backends use as const, satisfies, and other strange ways to export a simple object

If you've taken a look at ZenFS' code, you may have noticed just how convoluted an actual backend definition is:

const _InMemory = {
	// ...
} as const satisfies Backend<StoreFS<InMemoryStore>, { name?: string }>;
type _InMemory = typeof _InMemory;
export interface InMemory extends _InMemory {}
export const InMemory: InMemory = _InMemory;
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There are quite a few things going on here, but they are all for a good reason:

1. as const and satisfies: This is to make sure the backend has the strictest types Typescript will allow, which in turn allow for more detailed and precise information when you try to incorrectly configure a backend
2. type _... and interface: The type alias is needed since interfaces can't extend typeof types. Using an interface means when a backend is incorrectly configured, you will see the interface name. If this isn't done, VS Code and Typescript will show the entire expanded as const type definition in the error message.
3. Exporting with a different name: This is done since a type can not be referenced in its own definition

Integration with VFS and Internal API

The VFS does not interact directly with storage media. Instead, it mounts a configured backend, which in turn instantiates a FileSystem. This design ensures modularity and simplifies adding new storage types.