Convert a directory structure in the filesystem to JSON with Node.js

My CS example (w/ express) based on Miika's solution:

fs = require 'fs' #file system module
path = require 'path' # file path module

# returns json tree of directory structure
tree = (root) ->
    # clean trailing '/'(s)
    root = root.replace /\/+$/ , ""
    # extract tree ring if root exists
    if fs.existsSync root
        ring = fs.lstatSync root
    else
        return 'error: root does not exist'
    # type agnostic info
    info = 
        path: root
        name: path.basename(root)
    # dir   
    if ring.isDirectory()
        info.type = 'folder'
        # execute for each child and call tree recursively
        info.children = fs.readdirSync(root) .map (child) ->
            tree root + '/' + child
    # file
    else if ring.isFile()
        info.type = 'file'
    # link
    else if ring.isSymbolicLink()
        info.type = 'link'
    # other
    else
        info.type = 'unknown'
    # return tree 
    info

# error handling
handle = (e) ->
    return 'uncaught exception...'

exports.index = (req, res) ->
    try
        res.send tree './test/'
    catch e
        res.send handle e

there's an NPM Module for it

https://www.npmjs.com/package/directory-tree

Creates an object representing a directory tree.

From:

photos
├── summer
│   └── june
│       └── windsurf.jpg
└── winter
    └── january
        ├── ski.png
        └── snowboard.jpg

To:

{
  "path": "",
  "name": "photos",
  "type": "directory",
  "children": [
    {
      "path": "summer",
      "name": "summer",
      "type": "directory",
      "children": [
        {
          "path": "summer/june",
          "name": "june",
          "type": "directory",
          "children": [
            {
              "path": "summer/june/windsurf.jpg",
              "name": "windsurf.jpg",
              "type": "file"
            }
          ]
        }
      ]
    },
    {
      "path": "winter",
      "name": "winter",
      "type": "directory",
      "children": [
        {
          "path": "winter/january",
          "name": "january",
          "type": "directory",
          "children": [
            {
              "path": "winter/january/ski.png",
              "name": "ski.png",
              "type": "file"
            },
            {
              "path": "winter/january/snowboard.jpg",
              "name": "snowboard.jpg",
              "type": "file"
            }
          ]
        }
      ]
    }
  ]
}

Usage

var tree = directoryTree('/some/path');

And you can also filter by extensions:

var filteredTree = directoryTree('/some/path', ['.jpg', '.png']);

Here's a sketch. Error handling is left as an exercise for the reader.

var fs = require('fs'),
    path = require('path')

function dirTree(filename) {
    var stats = fs.lstatSync(filename),
        info = {
            path: filename,
            name: path.basename(filename)
        };

    if (stats.isDirectory()) {
        info.type = "folder";
        info.children = fs.readdirSync(filename).map(function(child) {
            return dirTree(filename + '/' + child);
        });
    } else {
        // Assuming it's a file. In real life it could be a symlink or
        // something else!
        info.type = "file";
    }

    return info;
}

if (module.parent == undefined) {
    // node dirTree.js ~/foo/bar
    var util = require('util');
    console.log(util.inspect(dirTree(process.argv[2]), false, null));
}

The accepted answer works, but it is synchronous and will deeply hurt your performance, especially for large directory trees.
I highly encourage you to use the following asynchronous solution, it is both faster and non-blocking.
Based on the parallel solution here.

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

var diretoryTreeToObj = function(dir, done) {
    var results = [];

    fs.readdir(dir, function(err, list) {
        if (err)
            return done(err);

        var pending = list.length;

        if (!pending)
            return done(null, {name: path.basename(dir), type: 'folder', children: results});

        list.forEach(function(file) {
            file = path.resolve(dir, file);
            fs.stat(file, function(err, stat) {
                if (stat && stat.isDirectory()) {
                    diretoryTreeToObj(file, function(err, res) {
                        results.push({
                            name: path.basename(file),
                            type: 'folder',
                            children: res
                        });
                        if (!--pending)
                            done(null, results);
                    });
                }
                else {
                    results.push({
                        type: 'file',
                        name: path.basename(file)
                    });
                    if (!--pending)
                        done(null, results);
                }
            });
        });
    });
};

Example usage:

var dirTree = ('/path/to/dir');

diretoryTreeToObj(dirTree, function(err, res){
    if(err)
        console.error(err);

    console.log(JSON.stringify(res));
});