Casting Objects to Class Instances in JavaScript
Question:
How can I cast a generic object array (e.g., [{personName: 'John', animals: []}]) received from a server to a typed array of objects (e.g., [Person(personName: 'John', animals: [])]), allowing for method use (e.g., persons[0].animals[2].run())?
Answer:
Creating class instances in JavaScript requires invoking the constructor with the correct arguments (not just properties). We provide two solutions:
Method 1: Static Method for Cloning
Define a static method on the class that takes objects and creates instances from them, for example:
<code class="javascript">Person.fromJSON = function(obj) { // Custom code for Person instances return new Person(); };</code>
Method 2: Object Cloning
Clone the properties from the JSON-parsed object to a new instance, for example:
<code class="javascript">var personLiteral = JSON.parse("..."); var personInstance = new Person(); for (var prop in personLiteral) personInstance[prop] = personLiteral[prop];</code>
Or, using Object.assign:
<code class="javascript">var personInstance = Object.assign(new Person(), personLiteral);</code>
Example for Your Case:
In your specific case, you have a simple object structure with no arguments and only public properties. To convert to an object instance:
<code class="javascript">var persons = JSON.parse(serverResponse); for (var i=0; i<persons.length; i++) { persons[i] = $.extend(new Person, persons[i]); for (var j=0; j<persons[i].animals; j++) { persons[i].animals[j] = $.extend(new Animal, persons[i].animals[j]); } }</code>
Note: The run method should likely be added to the Animal.prototype object instead of each instance.
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