Features

fs-backend uses a feature set instead of a capability record.

Why a Set

Backends expose optional support through:

type FileSystemBackendFeature = "write" | "mkdir" | "remove" | "copy";

and:

backend.features: ReadonlySet<FileSystemBackendFeature>

This keeps runtime checks simple and extensible.

Use hasFeature() when you want a readable runtime check before relying on a mutable operation:

import { hasFeature } from "@ucdjs/fs-backend";

if (hasFeature(backend, "write")) {
  await backend.write("/file.txt", "hello");
}

You can also check multiple features together:

if (hasFeature(backend, ["write", "mkdir"])) {
  await backend.mkdir("/nested/");
  await backend.write("/nested/file.txt", "hello");
}

Use assertFeature() when the operation is required for the current code path:

import { assertFeature } from "@ucdjs/fs-backend";

assertFeature(backend, "copy");
await backend.copy("/source.txt", "/copied.txt");

If the backend does not support that feature, assertFeature() throws BackendUnsupportedOperation.

if (!backend.features.has("write")) {
  console.log("This backend is read-only");
}

if (hasFeature(backend, ["write", "mkdir"])) {
  await backend.mkdir("/output/");
  await backend.write("/output/result.txt", "done");
}