De/serialize JS objects to and from Dicts, respecting arrays, nulls, etc.

Cakefile

{exec} = require 'child_process'

task "build", "Compile all CoffeeScript to JavaScript", ->
  exec 'coffee --bare --compile --join persistence-test.js ' +
    ("#{file}.coffee" for file in ["utilities", "persistence", "test"]).join(" "),
    (err, stdout, stderr) ->
      throw err if err
      console.log stdout + stderr

persistence-test.js

// Generated by CoffeeScript 1.6.2
var Persistence, bang, objectType, roundtrip;

objectType = function(object) {
  return Object.prototype.toString.call(object).match(/(\S+)]$/)[1];
};

Persistence = (function() {
  function Persistence() {}

  Persistence.prototype.serializeObject = function(object) {
    var dict, key, value;

    dict = new Dict;
    for (key in object) {
      value = object[key];
      if (value != null) {
        dict.set(key, !(value instanceof Object) ? value : this.serializeObject(value));
      }
    }
    return dict;
  };

  Persistence.prototype.deserializeObject = function(dict) {
    var isArray, key, keys, lastKey, object, value, _i, _len, _results;

    keys = this.normalizedKeys(dict);
    if (keys.length === 0) {
      return null;
    }
    object = new Object;
    isArray = true;
    lastKey = "-1";
    for (_i = 0, _len = keys.length; _i < _len; _i++) {
      key = keys[_i];
      if (!(key != null)) {
        continue;
      }
      value = dict.get(key);
      if (objectType(value) === "Dict") {
        value = this.deserializeObject(value);
      }
      object[key] = value;
      if (isArray) {
        if (parseInt(key) !== parseInt(lastKey) + 1) {
          isArray = false;
        }
        lastKey = key;
      }
    }
    if (!isArray) {
      return object;
    } else {
      _results = [];
      for (key in object) {
        value = object[key];
        _results.push(value);
      }
      return _results;
    }
  };

  Persistence.prototype.normalizedKeys = function(dict) {
    var keys;

    keys = dict.getkeys();
    if (keys == null) {
      keys = [];
    }
    if (!(keys instanceof Array)) {
      keys = [keys];
    }
    return keys;
  };

  return Persistence;

})();

bang = function() {
  post(JSON.stringify(roundtrip({
    just: "another",
    normal: "object"
  })));
  return post(JSON.stringify(roundtrip(["an", "array"])));
};

roundtrip = function(object) {
  return Persistence.prototype.deserializeObject(Persistence.prototype.serializeObject(object));
};

persistence-test.maxpat

{
  "patcher" : 	{
		"fileversion" : 1,
		"appversion" : 		{
			"major" : 6,
			"minor" : 1,
			"revision" : 2,
			"architecture" : "x86"
		}
,
		"rect" : [ 85.0, 69.0, 226.0, 128.0 ],
		"bglocked" : 0,
		"openinpresentation" : 0,
		"default_fontsize" : 12.0,
		"default_fontface" : 0,
		"default_fontname" : "Arial",
		"gridonopen" : 0,
		"gridsize" : [ 15.0, 15.0 ],
		"gridsnaponopen" : 0,
		"statusbarvisible" : 2,
		"toolbarvisible" : 1,
		"boxanimatetime" : 200,
		"imprint" : 0,
		"enablehscroll" : 1,
		"enablevscroll" : 1,
		"devicewidth" : 0.0,
		"description" : "",
		"digest" : "",
		"tags" : "",
		"boxes" : [ 			{
				"box" : 				{
					"id" : "obj-3",
					"maxclass" : "button",
					"numinlets" : 1,
					"numoutlets" : 1,
					"outlettype" : [ "bang" ],
					"patching_rect" : [ 30.0, 30.0, 20.0, 20.0 ]
				}

			}
, 			{
				"box" : 				{
					"fontname" : "Arial",
					"fontsize" : 12.0,
					"id" : "obj-1",
					"maxclass" : "newobj",
					"numinlets" : 1,
					"numoutlets" : 1,
					"outlettype" : [ "" ],
					"patching_rect" : [ 30.0, 60.0, 119.0, 20.0 ],
					"saved_object_attributes" : 					{
						"filename" : "persistence-test.js",
						"parameter_enable" : 0
					}
,
					"text" : "js persistence-test.js"
				}

			}
 ],
		"lines" : [ 			{
				"patchline" : 				{
					"destination" : [ "obj-1", 0 ],
					"disabled" : 0,
					"hidden" : 0,
					"source" : [ "obj-3", 0 ]
				}

			}
 ],
		"dependency_cache" : [ 			{
				"name" : "persistence-test.js",
				"bootpath" : "/Users/adam/projects/loom/dev/json-to-dict",
				"patcherrelativepath" : ".",
				"type" : "TEXT",
				"implicit" : 1
			}
 ]
	}

}

persistence.coffee

# 
# De/serialize JS objects to and from Dicts.
# 
# Copyright 2013 Adam Florin
# 

class Persistence
  
  # Utility: Feed Object into Dict structure, recursively.
  # 
  # Don't store null values.
  # 
  serializeObject: (object) ->
    dict = new Dict
    for key, value of object when value?
      dict.set(
        key, 
        unless value instanceof Object then value else @serializeObject value)
    return dict

  # Utility: Build Object from Dict structure, recursively.
  # 
  # Determine that dict should be built as an Array if all of its keys are
  # contiguous numbers beginning with "0".
  # 
  # If dict is empty, there's no way to determine if it's supposed to be an
  # array or object, so just return null so object can initialize that value.
  # 
  deserializeObject: (dict) ->
    keys = @normalizedKeys dict
    return null if keys.length == 0
    object = new Object
    isArray = true
    lastKey = "-1"
    for key in keys when key?
      value = dict.get(key)
      value = @deserializeObject(value) if objectType(value) is "Dict"
      object[key] = value
      if isArray
        isArray = false if parseInt(key) isnt parseInt(lastKey) + 1
        lastKey = key
    return unless isArray then object else (value for key, value of object)

  # The return value of getkeys() is unreliable, presumably because it was
  # designed for use in Max, not in JS. Return an array here, no matter
  # whether getkeys() returned an array, a single value, or null.
  # 
  normalizedKeys: (dict) ->
    keys = dict.getkeys()
    keys = [] unless keys?
    keys = [keys] unless keys instanceof Array
    return keys

test.coffee

# 
# test.coffee: expose functionality to Max for testing.
# 

# Run a few tests on bang.
# 
# Check the console for output
# 
bang = ->
  post JSON.stringify roundtrip
    just: "another"
    normal: "object"

  post JSON.stringify roundtrip ["an", "array"]

# Serialize a JS object to a Dict, then immediately deserialize it.
# 
roundtrip = (object) ->
  Persistence::deserializeObject Persistence::serializeObject object

utilities.coffee

# Get string representation of object type, but more precise than typeof.
# 
objectType = (object) ->
  Object::toString.call(object).match(/(\S+)]$/)[1]