Create subfilesystems that are rooted at a specific directory.

Node's filesystem api isn't very composable because you can't pass a filesystem referecne to a directory, you only can pass path prefixes to libraries that do something with the filesystem.

That approach has the downside that all those libraries require the fs module themselves, so they don't run on the client, because you can't pass in a custom filesystem instance (which could be backed by IndexDB or LocalStore for example). Yes, dependency injection.

So with this module, you can pass references to file system paths, that a module can treat as the root filesystem and can't write outside of (unless it's doing some magic native bindings stuff). Now you just need to encourage developers to accept subfs instances instead of paths in their modules!

var fs = require('fs');
var subfs = require('subfs');

var sub = subfs(fs, __dirname + '/dir');

// write file.txt into the filesystem mounted at ./dir
sub.writeFile('file.txt', 'foobar', function(err) {
  if (err) throw err;

  fs.readFile(__dirname + '/dir/file.txt', function(err, value) {
    if (err) throw err;
    console.log('value: %s', value);
    // value: foobar
  });
});

A module that consumes subfs could be called like this:

var fs = require('fs');
var subfs = require('subfs');
var Logs = require('your-logs-module');

var logs = Logs(subfs(fs, __dirname + '/logs'));

In the browser, initialize it like this:

var fs = require('level-fs-browser');
var subfs = require('subfs');
var Logs = require('your-logs-module');

var logs = Logs(subfs(fs, __dirname + '/logs'));

You just need to change one line!

var subfs = require('subfs');

Create a fs clone that prefixes each operation with the given dir.

With npm do:

npm install subfs

(MIT)

Copyright (c) 2013 Julian Gruber <julian@juliangruber.com>

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