merged-fs

Take several separate node filesystem implementations or filesystem aliases, and merges them into a single object that mimics the regular 'ol node fs module.

I put together as prototype to merge several Webpack MemoryFileSystems, so it is easier to use other code that directly relies on the node filesystem. It works, and is decently tested, but still early. Oh, and I'm assuming >= node 6.x for now.

Usage

const mergedFS = createMergedFileSystem({
  // Point a "mount point" to a specific filesystem impl, meaning that
  // `mergedFS.statSync('/mount-point-1/file.txt')` will end up calling
  // `customFSInstance.statSync('/file.txt')`
  "/mount-point-1": customFSInstance,

  // Make an alias, so that `/an-alias/dir/file.txt` ends up hitting `/some/path/dir/file.txt`
  // on the native filesystem
  "/an-alias": "/some/path",

  // Have fallbacks for a specific mount point
  "/another-mount-point": [
    customFSInstance2,
    customFSInstance3,
    "/some/fs/path"
  ],

  // Custom filesystem with an alias, so `/custom-fs-with-alias/dir/file.txt` will
  // hit `/teh-alias/dir/file.txt` of customFSInstance4
  "/custom-fs-with-alias": {
    alias: "teh-alias",
    filesystem: customFSInstance4
  },

  "/": "/",  // fallthrough to the native filesystem
  // OR 
  // "/": require('fs')
});

Details

So far, this only supports the following node filesystem APIs so far (both sync and async):

• stat
• readdir
• readFile
• readlink

And by default, all of those functions will return the first successful result after iterating through all the filesystems (in order of most to least specific). However, readdir will merge all the successful results together into a single array (representing all the files in any directory of a matching filesystem).

NOTE, intentionally completely ignoring windows paths and using unix-style paths (for now?)