JavaScript Class Definition

Class Definition in JavaScript

• Classes are defined using the class ClassName { ... } syntax.
• Include a constructor(params) method for initial object properties.
• Other methods can be defined within the class using the methodName() { ... } structure.

Types of Objects

• Functional Objects:

  • Fundamental since the inception of JavaScript.
  • Behave differently than objects in Java or C++.

• Classical Objects:

  • Introduced in 2015, they provide a more approachable syntax over functional objects.

Method References

• Other methods within the class are referred to using the this prefix to maintain context.

Public Fields

• Declare public fields directly in the class body:
  • Example:

    class Rectangle {
        height = 0;
        width;
    
        constructor(height, width) {
            this.height = height;
            this.width = width;
        }
    }
    

Private Fields

• Private fields use a # prefix:
  • Example:

    class Rectangle {
        #height = 0;
    
        constructor(height) {
            this.#height = height;
        }
    }
    

• Only accessible within the class body.

First-Class Functions

• Functions are treated as first-class citizens in JavaScript:
  • Can be passed as parameters.
  • Can be stored in variables.
  • Can be anonymous (no name).

Function Characteristics

• A function in JS is an object of type function, created using the function keyword.
• Must have parameters and a body wrapped in curly brackets, regardless of size.
• Can have multiple or no parameters and can be named or anonymous.

Function Properties

• Each function object has properties like name and toString().
  • Example:

    const greeting = function() {
        console.log('hello');
    };
    console.log(greeting.name); // Accesses the name property
    console.log(greeting.toString()); // Displays the function body as a string.
    

Function Call Method

• The call method invokes the code associated with a function object directly.

Function Invocation Syntax

• Using parentheses () on a function object calls its call() method, executing the underlying code.

Understanding Functions

• Distinction between the function (executable code) and the function object (a callable JS object).
• Functions can be invoked by name or using the call() method.

Special Status of Functions

• Functions can be invoked, unlike regular JavaScript objects.
• Regular JS objects can't execute code, which makes functions unique and special.