Prototypal Inheritance | Cheat Sheet

 1. Built-in Constructor Functions

These are the built-in constructor functions provided by JavaScript.

• function Array()
• function Function()
• function Promise()
• function Object()
• function String()
• function Number(), etc.

2. Built-in 

Array

 Constructor Function

2.1 Default Properties and Methods

Properties:

• constructor
• length
• prototype, etc.

Methods:

• push()
• pop()
• splice()
• shift(), etc.

2.2 Creating an Array with the 

new

 Operator (Older way of writing)

Syntax:

let myArray = new Array(item1, item2, ...);

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let myArray = new Array("a", 2, true);

myArray.push("pen");

console.log(myArray); // Array (4)["a", 2, true, "pen"]

console.log(myArray.length); // 4

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3. Prototype Property

The Prototype property will be shared across all the instances of their constructor function.

3.1 Accessing the Prototype of a Constructor Function

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console.log(Array.prototype);

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3.2 Accessing the shared Prototype of an Instance

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let myArray = new Array("a", 2, true);

console.log(Object.getPrototypeOf(myArray));

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3.3 Prototypal Inheritance

On calling the

new()

operator, all the properties and methods defined on the

prototype

will become accessible to the instance objects. This process is called Prototypal Inheritance.

4. Built-in 

Function

 Constructor Function

4.1 Default Properties and Methods

Properties:

• name
• length
• constructor
• prototype, etc.

Methods:

• apply()
• bind()
• call()
• toString(), etc.

4.2 Creating a Function with the 

new

 Operator (Older way of writing)

Syntax:

let myFunction = new Function("param1, param2, ...", function body);

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let Car = new Function("color, brand",

`this.color = color;

this.brand = brand;

this.start = function() {

console.log("started");

};`);

console.log(Function.prototype);

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5. Instance Specific and Prototype Properties

5.1 Prototype Properties/ Methods

The Prototype Properties/ Methods are the properties or methods common across the instance objects.

Examples:

• calculateAge
• displayGreetings
• displayProfileDetails
• calculateIncome

5.1.1 Adding a Method to the prototype

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function Person(firstName, lastName) {

this.firstName = firstName;

this.lastName = lastName;

}

Person.prototype.displayFullName = function() {

return this.firstName + " " + this.lastName;

};

let person1 = new Person("Virat", "Kohli");

let person2 = new Person("Sachin", "Tendulkar");

console.log(Object.getPrototypeOf(person1) === Object.getPrototypeOf(person2));

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5.2 Instance Specific Properties/ Methods

The Instance Specific Properties/ Methods are the properties or methods specific to the instance object.

Examples:

• gender
• yearOfBirth
• friendsList
• name

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function Person(firstName, lastName) {

this.firstName = firstName;

this.lastName = lastName;

}

Person.prototype.displayFullName = function() {

return this.firstName + " " + this.lastName;

};

let person1 = new Person("Virat", "Kohli");

console.log(Object.getOwnPropertyNames(person1));

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Examples : (How to add Prototype in Constructor Function)

Arithmetic Operations 

Given a constructor function ArithmeticOperations in the prefilled code and two numbers firstNumber and secondNumber as inputs, add the following methods to the constructor function using the prototype. Method Description ratioOfNumbers It Should return the ratio of the numbers sumOfCubesOfNumbers It Should return the sum of cubes of the numbers productOfSquaresOfNumbers It Should return the product of squares of the numbers.

Trekking Kit 

Given an object trekkingKit in the prefilled code and item item as an input, 

write a JS program to add the method isKitContains to the constructor function Trekking using the prototype. The method isKitContains checks whether the trekkingKit contains the given item .

Input The input will be a single line containing a string item Output The output should be a single line containing a boolean value.

The   Object.getOwnPropertyNames()   method gives an array containing the properties of the object.

This is How we can get prototype properties.