writing js objects to files (including methods) in nodejs?

Question

I see how I can write objects to files as described here: How can I save objects to files in Node.js? but is there a way to take an object and write it in a way that allows me to reload the object into memory including its methods?

Answer 1

As @AnthonySottile said before, this can be extremely dangerous and I'm not sure there is ever a good use case for it, but just for kicks and giggles you would need to write your own recursive serializer. Something like this:

var toString = Object.prototype.toString;

function dump_object(obj) {
    var buff, prop;
    buff = [];
    for (prop in obj) {
        buff.push(dump_to_string(prop) + ': ' + dump_to_string(obj[prop]))
    }
    return '{' + buff.join(', ') + '}';
}

function dump_array(arr) {
    var buff, i, len;
    buff = [];
    for (i=0, len=arr.length; i<len; i++) {
        buff.push(dump_to_string(arr[i]));
    }
    return '[' + buff.join(', ') + ']';
}

function dump_to_string(obj) {
    if (toString.call(obj) == '[object Function]') {
        return obj.toString();
    } else if (toString.call(obj) == '[object Array]') {
        return dump_array(obj);
    } else if (toString.call(obj) == '[object String]') {
        return '"' + obj.replace('"', '\\"') + '"';
    } else if (obj === Object(obj)) {
        return dump_object(obj);
    }
    return obj.toString();
}

This will handle most types, but there is always the chance of an oddball messing it up so I would not use this in production . Afterwards unserializing is as easy as:

eval('var test = ' + dump_to_string(obj))

Answer 2

The question is quite old, but I couldn't find anywhere some simple solution to the question of effective serialization in JavaScript.
One could use BSON (MongoDB inner objects representation) which uses a binary format to represent objects in memory.

I could not find some link to the documentation, but the code is well documented and I came up with something like this :

fs = require 'fs'
bson = require('bson').BSONPure.BSON

obj = {
  string: "test",
  func: (s) ->
    console.log s
}

fs.writeFile 'test.txt', bson.serialize(obj, false, false, true), (err) ->
  return console.log("Err : #{err}") if err
  fs.readFile 'test.txt', (err, file) ->
    return console.log("Err : #{err}") if err
    deserialized = bson.deserialize file, evalFunctions: true
    deserialized.func deserialized.string // Outputs 'text', as expected

It is coffee-script but the code is simple enough for everyone to understand.

Answer 3

I recently wrote shovejs: http://shovemedia.github.com/shovejs/ to handle exactly this sort of thing. YMMV -- I haven't tried it with Node yet.

It converts a typed object structure to JSON (which you'd then save to disk) and can inflate that structure back into typed objects including proper object -> object references etc. To be clear, the method / class definitions themselves are NOT serialized. The system simply expects that registered Model / Factory classes available during serialization are also available during deserialization.

Apologies in advance for not having some simple examples posted.

edit: the technique is a souped-up take on what Rob W mentions in his comment below