@file-services/overlay
v9.4.1
Published
Overlay files and directories from one file system on top of another.
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@file-services/overlay
Overlay files and directories from one file system on top of another.
Motivation
Overlay file system allows taking a native node file system ("lower fs") and overlay files and directories from an in-memory file system ("higher fs"). It can be used as a virtual layer providing a solution for storing and manipulating temporary data.
Behavior
Read operations (readFile
, readdir
, stat
, etc.) are checking higher fs first, and fallback to lower fs.
Currently, all write operations go directly to the original lower fs.
Getting started
Install library in project:
npm i @file-services/overlay
Then, use the programmatic API:
import { createOverlayFs } from "@file-services/overlay";
import { createMemoryFs } from "@file-services/memory";
import { nodeFs } from "@file-services/node";
const memFs = createMemoryFs({
src: {
"a.txt": `A`,
"b.txt": `B`,
},
});
const overlayFs = createOverlayFs(nodeFs /* lower fs */, memFs /* higher fs */);
// overlayFs.readFileSync('src/a.txt', 'utf8') === 'A'
createOverlayFs
also accepts a directory path as third parameter which specifies which directory in lower fs should be overlaid upon (defaults to lowerFs.cwd()
). This is important when overlaying a memory fs over native node fs and running on Windows. Memory fs uses posix-style paths, so the base directory is where memory's root /
begins to overlay.
License
MIT