How to write a complex object in memory to a file in nodejs

Question

I am creating a complex object dynamically with nodejs in an effort to write this data to a file for use as a frontend utility library.

Is there any way that I can read/write this object to a file?

Methods I am aware of that fall short:

JSON.stringify : need to output methods
jsDump : end up with [code] blocks for function body
writing my own 'recursive serializer'
trying to create a new Buffer from the object
Function.prototype.toString

I'm beginning to think that this is just not possible. Can anyone prove me wrong?

Note: As easy as it is to just read/concat/write files together with workable code for the browser, I would also like to be able to use this as an npm package. The library is set up in a fashion where each bit of reusable code is living in its own file. A build tool allows you to select which files you would like to include in the end result. The complex object I speak of is actually just a global namespace for all of the resulting functionality.

Edit for clarity

Resulting object stored in memory

var obj = {
  foo: 'a string',
  reg: /\s+/,
  num: 100,
  fart: function (name) {
    return name + ' farted and it sounded like pffftt';
  },
  Fart: function (sound) {
    this.sound = sound;
  }
};

And then you write that object character-for-character in a file for use in a browser.

@Mörre yes, I agree. The question here is if it is possible to read that data (the object in it's entirety) in memory and write it to a file. — davidg
– davidg, Commented Oct 27, 2013 at 9:40
No of course not, since you don't have memory level access in this language. You spent too much time with C(++) :-) — Mörre
– Mörre, Commented Oct 27, 2013 at 9:41
Sorry to spoil it. But if you really insist, just use JSON stringify and function's toString() - why not? By the way "char for char" does not work simply because that object isn't a linear structure in memory. Each function is another complete object, any variable pointing to an object rather than a primitive JS type is just a (C) pointer to other memory. So sequentially reading would do even LESS than JSON stringify, which catches things like Arrays and sub-objects. — Mörre
– Mörre, Commented Oct 27, 2013 at 9:45

vkurchatkin · Accepted Answer · 2013-10-27 13:08:49Z

Here is a demo, which covers your test case: http://jsfiddle.net/ZFUws/.

function isArray (obj) { return Array.isArray(obj); }

function isObject (obj) { //detect only simple objects
    return obj.__proto_ === Object.prototype;
}

function each (obj, iterator) {
    for (var key in obj) if (obj.hasOwnProperty(key)) iterator(obj[key]);
}

function map (obj, iterator) {
    if (Array.isArray(obj)) return obj.map(iterator);

    var newObj = {};
    for (var key in obj) if (obj.hasOwnProperty(key)) newObj[key] = iterator(obj[key]);
    return newObj;
}

var special = {
    'regexp' : {
        match : function (obj) {
            return obj instanceof RegExp; 
        },
        serialize : function (obj) {
            return {
                $class : 'regexp',
                source : obj.source,
                global : obj.global,
                multiline : obj.multiline,
                lastIndex : obj.lastIndex,
                ignoreCase : obj.ignoreCase
            } 
        },
        deserialize : function (json) {
            var flags = '',
                regexp;

            flags += json.global ? 'g' : '';
            flags += json.multiline ? 'm' : '';
            flags += json.ignoreCase ? 'i' : '';

            regexp = new RegExp(json.source, flags);

            regexp.lastIndex = json.lastIndex

            return regexp;
        }
    },
    'function' : {
        match : function (obj) {
            return obj instanceof Function; 
        },
        serialize : function (obj) {
            return {
                $class : 'function',
                source : obj.toString()
            } 
        },
        deserialize : function (json) {
            return (new Function('return ' + json.source))();
        }
    }
}

function toJSON (obj) {
    return map(obj, function (val) {
        var json;

        each(special, function (desc) {
            if (desc.match(val)) json = desc.serialize(val); 
        });

        if (isArray(val) || isObject (val)) json = toJSON(val);

        return json ? json : val;
    });
}

function fromJSON (json) {
    return map(json, function (val) {
        var obj;

        if (val.$class) {
            obj = special[val.$class].deserialize(val);
        }

        if (isArray(val) || isObject (val)) obj = fromJSON(val);

        return obj ? obj : val;
    });
}

var obj = {
  foo: 'a string',
  reg: /\s+/,
  num: 100,
  fart: function (name) {
    return name + ' farted and it sounded like pffftt';
  },
  Fart: function (sound) {
    this.sound = sound;
  }
};

var serialized = JSON.stringify(toJSON(obj)),
    deserialized = fromJSON(JSON.parse(serialized));

console.log(deserialized.foo);
console.log(deserialized.num);
console.log('11    '.search(deserialized.reg));
console.log(deserialized.fart('John'));
console.log(new deserialized.Fart('pffftt').sound);

Thanks for your effort! I'll implement this and see how it writes to a file and post the result.

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