The constructor method is a special method within a JavaScript class specifically for creating and initializing an object instance of that class. When a new instance is created using the new keyword (e.g., new Post(...)), the constructor is automatically called.

The provided code requires initializing the body, author, and viewCount properties. By defining constructor(body, author, viewCount), the class can accept these three values as arguments during instantiation. Inside the constructor, this refers to the new object being created, and this.property = value assigns the passed-in arguments to the corresponding properties of the new instance.

Why Incorrect Options are Wrong

A. super (body, author, viewCount) {

The super keyword is used to call the constructor of a parent class within a subclass, not to define the constructor for the current class.

B. Function Post (body, author, viewCount) {

This syntax defines a traditional constructor function (pre-ES6). It is not the correct syntax for defining a constructor method inside an ES6 class declaration.

D. constructor() {

This defines a constructor that accepts no parameters. The subsequent lines would cause a ReferenceError because the variables body, author, and viewCount would be undefined.

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References

1. Mozilla Developer Network (MDN) Web Docs:

Source: constructor - JavaScript | MDN

Reference: In the "Syntax" and "Description" sections, it is explicitly stated: "The constructor method is a special method of a class for creating and initializing an object instance of that class... There can be only one special method with the name 'constructor' in a class." The examples provided match the correct answer's syntax.

2. ECMAScript® 2023 Language Specification (ECMA-262, 14th edition):

Source: ECMA-262, 14th Edition, June 2023

Reference: Section 15.7.1, "Static Semantics: IsConstructor". This section defines the formal grammar for a class constructor. It specifies that a MethodDefinition within a ClassBody is a constructor if its PropName is "constructor". This confirms that constructor is the required, reserved keyword.

3. The Modern JavaScript Tutorial (javascript.info):

Source: Class basic syntax

Reference: In the section "What is a class?", the article states, "The constructor() method is called automatically by new, so we can initialize the object there." The provided examples clearly show the constructor(parameters) { ... } syntax for initializing object properties. This resource is widely referenced in academic curricula.