Serialise polymorphic JavaScript objects

Question

Conceptually, my app has an interface and many objects that implement the interface in different ways. The objects will be created by various factory methods, and there will be more factories in future as my app evolves.

For example

var Shapes={};
var Shapes.createCircle=function(radius) {
  return {draw:function...}
};
var Shapes.createRectangle=function(width,height) {
  return {draw:function...}
};

I want to serialize these shapes in files. I plan to make each object store the name of its factory (e.g. "Shapes.createRectangle") and an array of arguments (e.g [10,20]), and then save these parts as a JSON string. That way, the deserialized objects can have all their functions restored, as well as their properties.

For example, to save an object I plan to store the JSON string

{"factory":"Shapes.createRectangle","args":[10,20]}

and then reconstruct the object in a future sessions by dynamically calling the factory method again.

Does this method of serializing polymorphic objects have any gotchas?

Answer 1

Potentially. It will only work if these objects are immutable or if the only way you can change their state is reversible back into the factory arguments.

This tends to prove tricky as an api grows, but isn't impossible. I would check if an object has a serialize and deserialize method and invoke those, so you have a nice pattern how to customize serialization behavior if you need it in the future.

Answer 2

One drawback is, that you're hard-coding the factory function names into your data. Of course that's only a problem if you later decide to change them... Maybe just storing the object type would be more resilient to such problems.