JavaScript Class Definition
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Questions and Answers

What syntax do we use to define classes in JavaScript?

class ClassName { constructor (params) { } methodName() { } }

What are the two types of objects in JavaScript?

  • Functional (correct)
  • Classical (correct)
  • Dynamic
  • Static

    • How must you refer to other methods in the class?

    this.

    How can we declare public fields?

    <p>Class rectangle { height = 0; width; constructor(height, width) { this.height = height; this.width = width; }}</p> Signup and view all the answers

    How can we declare private fields?

    <p>Class rectangle { #height = 0; this.#height = height; }</p> Signup and view all the answers

    What are first class functions?

    <p>Functions that are treated like variables of type function.</p> Signup and view all the answers

    What is a function in JavaScript?

    <p>A function is an object of type function created with an expression starting with the keyword function.</p> Signup and view all the answers

    What are the properties of a function?

    <p>Functions have properties like name and toString().</p> Signup and view all the answers

    What does the call method do in a function?

    <p>Invokes the underlying executable code associated with this function object.</p> Signup and view all the answers

    What does () do in a function?

    <p>It calls the function's call() method which executes the underlying code.</p> Signup and view all the answers

    What is the difference between a function and a function object?

    <p>A function is executable code, while a function object is a JS object with executable code that can be invoked.</p> Signup and view all the answers

    Regular JavaScript objects can be invoked.

    <p>False</p> Signup and view all the answers

    Study Notes

    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.

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    Quiz Team

    Description

    Explore the intricacies of class definitions in JavaScript. This quiz covers topics such as constructors, public and private fields, and different types of objects. Test your understanding of JavaScript's class-based syntax and object-oriented programming concepts.

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