This document describes the high-level architecture of fdir. If you want to familiarize yourself with the code base, you are in the right place!
On the highest level, fdir is a library that accepts a path to a directory as input and outputs all the file paths in that directory recrusively.
More specifically, input data consists of a path to a directory (rootDirectory) and different flags and filters to control the walking process. To increase performance, fdir builds internal functions conditionally based on the passed flags. Since these "conditional" functions are tiny, they are inlined by the Javascript Engine reducing branching & allocations.
index.js exports the main fdir class and it is the main entry point. However, there is nothing of importance in this file aside from the export.
src/builder/index.js contains the main API of fdir exposed via a Builder class. This is where all the flags & filters are built and passed (as an options Object) onto the core of fdir.
This section talks briefly about all the directories and what each file in each directory does.
This is the core of fdir.
walker.js: This contains the Walker class which is responsible for controlling and maintaining the state of the directory walker. It builds the conditional functions, processes the Dirents and delegates the actual filesystem directory reading to sync/async APIs.
async.js This contains the asynchronous (fs.readdir) logic. This is the starting point of the async crawling process.
queue.js This contains a tiny Queue class to make sure fdir doesn't early exit during walking. It increments a counter for each "walk" queued and decrements it when it finishes. Once the counter hits 0, it calls the callback which returns the output to the user.
sync.js This contains the synchronous (fs.readdirSync) logic. This is the starting point of the sync crawling process.
fns.js This contains the implementations of all the conditional functions.
This is what gets exposed to the developer and contains 2 builders that aid in building an options object to control various aspects of the walker.
Since fdir supports Node <= 10.0, this directory contains the compatibility code to bridge the newer (v10.0) filesystem API with the older (v8.0) filesystem API.