Javascript Classes MCQ

In object-oriented programming, a class is a template for creating objects.
An object is an instance of a class, and it has the same behavior as defined by the class.
The class defines the properties and methods that the object will have, and the object is created based on that template.
All objects of the same class have the same behavior, but they can have different property values.
For example, you could have a class called "Dog" that defines the behavior of a dog, such as barking and wagging its tail.
You could then create multiple objects of the "Dog" class, each representing a different individual dog with its own unique characteristics, such as breed and name.

In object-oriented programming, the this keyword is used to refer to the current object. It is commonly used inside the body of a class's methods to refer to the object on which the method is being called.

For example, consider the following class:

class Person { constructor(name) {
this.name = name;
}

sayHello() {
console.log(`Hello, my name is ${this.name}`);
}
}


Here, the Person class has a constructor function that takes a name parameter and assigns it to the name property of the object being created.
The class also has a method called sayHello that prints a greeting to the console using the name property of the object.

In object-oriented programming, a constructor is a special method that is used to create and initialize an object created from a class.

In the example you provided, the Person class has a constructor function defined with the constructor keyword.
The constructor function takes a name parameter and assigns it to the name property of the object being created.

An object can be created from a class using the new keyword, followed by the name of the class and parentheses.
When an object is created using the new keyword, the class's constructor function is automatically called to initialize the object.
For example:
const person1 = new Person('Alice');
const person2 = new Person('Bob');
Here, two objects are created from the Person class using the new keyword. This causes the class's constructor function to be called twice, once for each object, initializing each object with its own name property.
So in this example, both statements const person1 = new Person('Alice'); and const person2 = new Person('Bob'); create an instance of the Person class, also known as an object

Java is a general-purpose, object-oriented programming language that is specifically designed to have as few implementation dependencies as possible. It is intended to let developers "write once, run anywhere" (WORA), meaning that compiled Java code can run on all platforms that support Java without the need for recompilation.

JavaScript, on the other hand, is a lightweight, interpreted programming language that is mainly used to create interactive effects within web browsers. It is a scripting language, which means that it is usually embedded in HTML pages and is interpreted by the web browser at runtime, rather than being compiled like a traditional programming language.

One of the main differences between Java and JavaScript is that in Java, functions are associated with classes and are called methods, while in JavaScript, functions are values that can be assigned to variables and passed as arguments to other functions. JavaScript also does not have a hard distinction between methods and fields, meaning that properties of an object can be either data or functions.

Another difference is that Java is a statically-typed language, while JavaScript is a dynamically-typed language. This means that in Java, variables must be declared with a specific type, and the type cannot be changed at runtime, while in JavaScript, the type of a variable is determined at runtime based on the value it is assigned.

In JavaScript, inheritance is implemented using prototypes, which are objects that serve as templates for creating other objects. When an object is created, it inherits properties and methods from its prototype, which can be another object or null. This is known as prototype-based inheritance.
One of the characteristics of prototype-based inheritance in JavaScript is that it is dynamic. This means that the prototype of an object can be changed at any time, and the changes will be reflected in all objects that inherit from it.
This is different from classical inheritance in languages like Java, where the inheritance hierarchy is fixed at the time the object is created and cannot be changed later.
In JavaScript, we can augment a class (which is implemented as a constructor function) by adding new methods to its prototype object.
For example: function Person(name) {
this.name = name;
}

Person.prototype.sayHello = function() {
console.log(`Hello, my name is ${this.name}`);
}

const person = new Person('Alice');
person.sayHello(); // Output: "Hello, my name is Alice"
Here, we define a Person constructor function that takes a name parameter and assigns it to the name property of the object being created.
We then add a sayHello method to the Person prototype object. When we create a new Person object using the new keyword, the object inherits the sayHello method from its prototype, so we can call it on the object.

JSON (JavaScript Object Notation) is a lightweight data interchange format that is easy for humans to read and write and easy for machines to parse and generate. It is based on a subset of the JavaScript programming language, and it is commonly used to transmit data between a server and a web application or between different components of a distributed application.

One common use of JSON is to exchange data between a web server and a client, such as a web browser. When sending data to a server, the data has to be in the form of a string. The JSON.stringify() method can be used to convert a JavaScript object or array into a JSON string.
For example:
const data = {
name: 'Alice',
age: 30
};

const dataString = JSON.stringify(data);
console.log(dataString); // Output: '{"name":"Alice","age":30}'

Here, the data object is converted into a JSON string using the JSON.stringify() method. The resulting string can then be sent to a server using an HTTP request.

In object-oriented programming, a subclass is a class that is derived from another class, called the superclass. The subclass inherits properties and methods from the superclass and can also have additional properties and methods of its own.
The subclass is also called an extension of the superclass, because it extends the functionality of the superclass with additional features.

For example, consider the following class hierarchy:
class A {
// Properties and methods of class A
}

class B extends A {
// Properties and methods of class B
}

Here, A is the superclass and B is the subclass. B is derived from A and inherits all of the properties and methods of A. B can also have additional properties and methods of its own.

In this example, A is the superclass and B is the subclass. In the scenario you described, A would also be the superclass and B would be the subclass.

In JavaScript, inheritance is implemented using prototypes, which are objects that serve as templates for creating other objects. There is no built-in inherit() function in JavaScript that allows one class to inherit from another, but you can achieve inheritance by setting up the prototype chain correctly.

To inherit from a superclass in JavaScript, you can use the Object.create() method to create a new object that has the superclass as its prototype. The new object will then inherit all of the properties and methods of the superclass.

For example:

function A() {
// Properties and methods of class A
}

A.prototype.sayHello = function() {
console.log('Hello from A');
}

function B() {
// Properties and methods of class B
}

// Set up inheritance
B.prototype = Object.create(A.prototype);

const b = new B();
b.sayHello(); // Output: "Hello from A"


Here, the B class is defined as a constructor function. The B prototype is then set to a new object that has the A prototype as its prototype using the Object.create() method.
This causes the B prototype to inherit all of the properties and methods of the A prototype, including the sayHello method. When we create a new B object using the new keyword, the object inherits the sayHello method from the B prototype, which in turn inherited it from the A prototype.

The instanceof operator is a JavaScript operator that is used to check if an object is an instance of a particular class or constructor function. It returns a boolean value indicating whether the object is an instance of the class or not.
The instanceof operator is written with the syntax object instanceof Class, where object is the object to be checked and Class is the constructor function or class to check against.
For example:
function A() {
// Properties and methods of class A
}

function B() {
// Properties and methods of class B
}

const a = new A();
console.log(a instanceof A); // Output: true
console.log(a instanceof B); // Output: false

const b = new B();
console.log(b instanceof A); // Output: false
console.log(b instanceof B); // Output: true

Here, we define two classes, A and B, and create two objects, a and b, using the new keyword. The instanceof operator is used to check if the objects are instances of the respective classes.
The first object, a, is an instance of A but not B, so the first two instanceof checks return true and false, respectively. The second object, b, is an instance of B but not A, so the last two instanceof checks return false and true, respectively.
The instanceof operator is useful for determining the type of an object at runtime and for implementing type checking in JavaScript programs.

The Object.defineProperty() method is used to define a new property on an object, or to modify an existing property on an object. It returns the object. Both Object.defineProperty() and Object.defineProperties() can be used to define new properties on an object.

The Object.assign() method is used to copy the properties and values from one or more source objects to a target object. It returns the target object. When objects are assigned or copied using Object.assign(), they are assigned or copied by reference, meaning that the target object and the source object refer to the same underlying object in memory.

The Object.create() method is used to create a new object with the specified properties. It is a way of creating a new object using an existing object as the prototype. The Object.create() method accepts two arguments: the prototype object and an optional property descriptor object.

The prototype object is the object that the newly created object will inherit from. The property descriptor object is optional and can be used to specify the characteristics of the properties to be added to the new object.

For example:

The Object.defineProperties() method is a predefined function in the object library of JavaScript that is used to define new properties or modify existing properties on an object. It returns the object.
The Object.defineProperties() method takes an object as its first argument and a property descriptor object as its second argument. The property descriptor object can specify the characteristics of one or more properties to be added to or modified on the object.

The Object.getPrototypeOf() method in JavaScript is used to get the prototype of an object. It returns the value of the prototype, which is the object that the object inherits properties and methods from.
The Object.getPrototypeOf() method does not return inherited properties of the object, only the prototype value.

The Object.seal() method in JavaScript is used to seal an object, which means that it prevents new properties from being added to the object and marks all existing properties as non-configurable. Sealed objects cannot be deleted, and their existing properties cannot be changed or removed.

To seal an object, you pass the object as an argument to the Object.seal() method and it returns the sealed object.

A class in object-oriented programming typically contains data members (also called instance variables) and associated member functions (also called instance methods). These data members and member functions make up the class's instance fields and instance methods, respectively.

In addition to instance fields and instance methods, a class can also have class fields and class methods, which are shared by all instances of the class. Overall, a class can have four kinds of members: instance fields, instance methods, class fields, and class methods.

In JavaScript, there are three different objects involved in the definition of a class: the constructor object, the prototype object, and the instance object. These objects have properties that act like different kinds of class members.

The constructor object is the function that is used to create an instance of the class. It has properties that act like instance fields and instance methods.

The prototype object is an object that is shared by all instances of the class and has properties that act like class fields and class methods.

The instance object is an object that represents a single instance of the class and has properties that act like instance fields and instance methods.

The properties of the prototype object in a JavaScript class are inherited by all instances of the class. This means that the properties are shared by all instances and can be accessed using the . notation.
Properties whose values are functions behave like instance methods of the class, which means that they can be called on instances of the class using the . notation.

Variable properties are variables that are associated with an object and can be accessed using the '.' notation. These variables can be used internally within the object's methods, or they can be globally visible and used throughout the page.

A regular expression is a pattern of characters that is used to match character combinations in strings. In JavaScript, regular expressions are represented using the RegExp class. The RegExp class provides methods for working with regular expressions, such as test(), exec(), and match().

Both strings and the RegExp class have methods that use regular expressions. For example, the String.prototype.match() method returns an array of strings that match a given regular expression, and the String.prototype.replace() method replaces substrings that match a given regular expression with a replacement string.

Regular expressions are a powerful tool for pattern matching and string manipulation in JavaScript. They are often used to validate user input, search and replace text, and extract data from strings.

The Object.prototype.constructor property specifies the function that creates the object prototype. It is a property of the Object.prototype object, which is the prototype of all objects in JavaScript.

In the code snippet you provided, the constructor property is being used to return a complex number that is the complex conjugate of the current complex number. A complex conjugate is a mathematical operation that negates the imaginary part of a complex number.

It is possible to add methods to the Object.prototype object in JavaScript, which makes them available on all objects. This can be done using the Object.defineProperty() method or by assigning a new property directly to the Object.prototype object.

Whether or not classes defined by the host environment (such as web browsers) can be augmented using Object.prototype depends on the implementation. In some cases, it may be possible to add methods to the prototype of a class and have those methods be inherited by objects that represent instances of the class.
For example, in many web browsers, it is possible to add methods to HTMLElement.prototype and have those methods be inherited by the objects that represent HTML tags in the current document.

The reload() method is a method of the Location object in JavaScript, which is used to reload the current page from the server. It can be called using the location.reload() notation.

An object is created by calling a function and passing it some arguments. The function uses the this keyword to set the values of the object's properties based on the arguments that were passed.

The emp function is defined as a constructor function that takes two arguments: name and salary.
The name and salary properties of the object are set using the this keyword.
The changeSalary method is defined and assigned to the changeSalary property of the object using the this keyword. The changeSalary method takes a single argument: otherSalary.
An object is created using the emp constructor function and passing it the arguments "Rahul" and 30000. 
This creates an object with the name property set to "Rahul" and the salary property set to 30000.
The changeSalary method is called on the object, passing it the argument 45000. This sets the salary property of the object to 45000.
The name and salary properties of the object are written to the document using the document.write() method. The output is e.name+ 45000.


The changeSalary method uses the this keyword to refer to the current object and sets the salary property of the object to the value of the otherSalary argument. 
This allows you to change the salary of the object by calling the changeSalary method and passing it a new salary value

The Object.entries() method is a built-in method in JavaScript that returns an array of a given object's own enumerable property [key, value] pairs. The order of the properties in the array is the same as the order in which they are enumerated in a for...in loop over the object.

"The Dojo toolkit and Google's Closure library both have functions called provide() and require() that are used for declaring and loading modules."

Modules are generally designed to run in an unmodified (or almost unmodified) environment, and should minimize the number of global symbols they define, with the goal of having no module define more than one.

"A singleton is a type of object that can only be created once. The extend keyword is used to create a child class from a parent class in class declarations or expressions.
In this case, the sets object serves as the namespace for the module, and the set classes are defined as properties of this object

The scope of a function can be used as a private namespace for a module, so the scope of a function in this context is referred to as a module function.

"A namespace is a container that holds a set of identifiers, functions, methods, and other elements and helps to organize and distinguish them.
Modules that have multiple items in their API may return a namespace object