Javascript: stringify object (including members of type function)

Question

I'm looking for a solution to serialize (and unserialize) Javascript objects to a string across browsers, including members of the object that happen to be functions. A typical object will look like this:

{
   color: 'red',
   doSomething: function (arg) {
        alert('Do someting called with ' + arg);
   }
}

doSomething() will only contain local variables (no need to also serialize the calling context!).

JSON.stringify() will ignore the 'doSomething' member because it's a function. I known the toSource() method will do what I want but it's FF specific.

Answer 1

A quick and dirty way would be like this:

Object.prototype.toJSON = function() {
  var sobj = {}, i;
  for (i in this) 
    if (this.hasOwnProperty(i))
      sobj[i] = typeof this[i] == 'function' ?
        this[i].toString() : this[i];

 return sobj;

};

Obviously this will affect the serialization of every object in your code, and could trip up niave code using unfiltered for in loops. The "proper" way would be to write a recursive function that would add the toJSON function on all the descendent members of any given object, dealing with circular references and such. However, assuming single threaded Javascript (no Web Workers), this method should work and not produce any unintended side effects

function JSONstringifyWithFuncs(obj) {
  Object.prototype.toJSON = function() {
    var sobj = {}, i;
    for (i in this) 
      if (this.hasOwnProperty(i))
        sobj[i] = typeof this[i] == 'function' ?
          this[i].toString() : this[i];

    return sobj;
  };

  var str = JSON.stringify(obj);

  delete Object.prototype.toJSON;

  return str;
}

Try it out: http://jsbin.com/ifafa3/6/edit

Answer 2

Something like this...

(function(o) {
    var s = "";
    for (var x in o) {
        s += x + ": " + o[x] + "\n";
    }
    return s;
})(obj)

Note: this is an expression. It returns a string representation of the object that is passed in as an argument (in my example, I'm passing the in an variable named obj).

You can also override the toString method of the Object's prototype:

Object.prototype.toString = function() {
    // define what string you want to return when toString is called on objects
}

Answer 3

It's impossible without the help of the object itself. For example, how would you serialize the result of this expression?

(function () {
  var x; 
  return {
      get: function () { return x; },
      set: function (y) { return x = y; }
    };
})();

If you just take the text of the function, then when you deserialize, x will refer to the global variable, not one in a closure. Also, if your function closes over browser state (like a reference to a div), you'd have to think about what you want that to mean.

You can, of course, write your own methods specific to individual objects that encode what semantics you want references to other objects to have.