How to Convert Plain JSON Objects into Class Instances in JavaScript?

Casting Plain Objects to Class Instances in JavaScript

In JavaScript, when receiving plain objects from a server as JSON responses, you may encounter the need to cast them into typed class instances. This allows you to access class-specific methods and properties.

Solution:

One approach is to create a constructor that accepts any object resembling an instance and clones it. Alternatively, you can implement a static method that converts objects to instances:

<code class="javascript">Person.fromJSON = function(obj) {
    // Custom code to create an instance from the object
    return ...;
};</code>

For your specific scenario, where you have plain objects with public properties, you can use the following method:

<code class="javascript">var personInstance = new Person();
for (var prop in personLiteral) {
    personInstance[prop] = personLiteral[prop];
}</code>

This assigns all properties from the plain object to the newly created instance. Similarly, you can create Animal instances.

Note:

• JSON does not provide class information, so you must know the object structure beforehand.
• It's recommended to move the run method to the Animal.prototype object rather than keeping it on each instance.

Sample Code:

<code class="javascript">var persons = JSON.parse(serverResponse);
for (var i = 0; i < persons.length; i++) {
    persons[i] = Object.assign(new Person(), persons[i]); // Use Object.assign for browsers that support it
    for (var j = 0; j < persons[i].animals; j++) {
        persons[i].animals[j] = Object.assign(new Animal(), persons[i].animals[j]);
    }
}</code>

This code will enable you to use class-specific methods such as persons[0].Animals[2].Run();.

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