Unraveling a JavaScript object derived from an unknown class: a comprehensive guide

Question

Unraveling a JavaScript object derived from an unknown class: a comprehensive guide

After finding a solution for serializing objects with known types in Javascript Serialization of Typed Objects, I now face a new challenge. I have an object of an unknown type that needs to be deserialized by code that is unaware of its specific type. The "Sprite" base class has properties that require serialization, with various derived classes like "Player" and "Platform" adding their own properties. Additionally, there is a "MapLayer" containing Sprite-derived objects. How can I ensure that each sprite will be correctly deserialized into its appropriate derived type? Should I resort to using eval("new " + derivedTypeName + parameterList)? Are there better alternatives?

Here are more specifics: Although the Sprite base class is fixed, all derived classes are generated dynamically. While I can make the code generator create deserialize functions for each derived class, how can I invoke them accordingly from the generic base class deserialization function? The single MapLayer class must somehow trigger the deserialize function for every class derived from Sprite.

javascript json serialization

Answer 1

Answer №1

If you want to invoke the constructor function of the derived object, you must first determine which constructor to use. Without specific information on how you are currently encoding this type data in your serialized payload, let's assume a setup similar to the one below:

var MyDerivedType = function () {...};
MyDerivedType.prototype.__derivedTypeName = 'MyDerivedType';
MyDerivedType.deserialize = function (input) {
    var obj = JSON.parse(input);
    return new MyDerivedType(obj);
};

If your derived types are not globally accessible, you will need a way to access them during deserialization. Storing them directly on the constructor itself, like so:

Sprite.derivedTypes = Sprite.derivedTypes || {};
Sprite.derivedTypes['MyDerivedType'] = MyDerivedType;

This approach eliminates the need for using `eval` and allows for calling the appropriate deserializer as shown below:

Sprite.deserialize = function(input) {

    // Parse the input string into JSON to extract the derived type
    var o = JSON.parse(input);

    // Call the deserialize method specific to the derived type
    return Sprite.derivedTypes[o.__derivedTypeName].deserialize(input);
};

It's important to note that JavaScript/browser environments do not natively provide deserialization to "classes" in the traditional sense found in languages like .net.

Answer 2

If you want to invoke the constructor function of the derived object, you must first determine which constructor to use. Without specific information on how you are currently encoding this type data in your serialized payload, let's assume a setup similar to the one below:

var MyDerivedType = function () {...};
MyDerivedType.prototype.__derivedTypeName = 'MyDerivedType';
MyDerivedType.deserialize = function (input) {
    var obj = JSON.parse(input);
    return new MyDerivedType(obj);
};

If your derived types are not globally accessible, you will need a way to access them during deserialization. Storing them directly on the constructor itself, like so:

Sprite.derivedTypes = Sprite.derivedTypes || {};
Sprite.derivedTypes['MyDerivedType'] = MyDerivedType;

This approach eliminates the need for using `eval` and allows for calling the appropriate deserializer as shown below:

Sprite.deserialize = function(input) {

    // Parse the input string into JSON to extract the derived type
    var o = JSON.parse(input);

    // Call the deserialize method specific to the derived type
    return Sprite.derivedTypes[o.__derivedTypeName].deserialize(input);
};

It's important to note that JavaScript/browser environments do not natively provide deserialization to "classes" in the traditional sense found in languages like .net.

Unraveling a JavaScript object derived from an unknown class: a comprehensive guide

Answer №1

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