JavaScript Constructor Function Explained with Examples

JavaScript Constructor Function Explained with Examples

In this tutorial, you will learn about JavaScript constructor function with the help of examples.

In JavaScript, a constructor function is used to create objects. For example,

// constructor function
function Person () {
    this.name = 'John',
    this.age = 23
}

// create an object
const person = new Person();

In the above example, function Person() is an object constructor function.

To create an object from a constructor function, we use the new keyword.

Note: It is considered a good practice to capitalize the first letter of your constructor function.

Create Multiple Objects with Constructor Function

In JavaScript, you can create multiple objects from a constructor function. For example,

// constructor function
function Person () {
    this.name = 'John',
    this.age = 23,

     this.greet = function () {
        console.log('hello');
    }
}

// create objects
const person1 = new Person();
const person2 = new Person();

// access properties
console.log(person1.name);  // John
console.log(person2.name);  // John

In the above program, two objects are created using the same constructor function.

JavaScript this Keyword

In JavaScript, when this keyword is used in a constructor function, this refers to the object when the object is created. For example,

// constructor function
function Person () {
    this.name = 'John',
}

// create object
const person1 = new Person();

// access properties
console.log(person1.name);  // John

Hence, when an object accesses the properties, it can directly access the property as person1.name.

JavaScript Constructor Function Parameters

You can also create a constructor function with parameters. For example,

// constructor function
function Person (person_name, person_age, person_gender) {

   // assigning  parameter values to the calling object
    this.name = person_name,
    this.age = person_age,
    this.gender = person_gender,

    this.greet = function () {
        return ('Hi' + ' ' + this.name);
    }
}


// creating objects
const person1 = new Person('John', 23, 'male');
const person2 = new Person('Sam', 25, 'female');

// accessing properties
console.log(person1.name); // "John"
console.log(person2.name); // "Sam"

In the above example, we have passed arguments to the constructor function during the creation of the object.

const person1 = new Person('John', 23, 'male');
const person2 = new Person('Sam', 25, 'male');

This allows each object to have different properties. As shown above,

console.log(person1.name); gives John

console.log(person2.name); gives Sam

Create Objects: Constructor Function Vs Object Literal

• Object Literal is generally used to create a single object. The constructor function is useful if you want to create multiple objects. For example,

// using object literal
let person = {
    name: 'Sam'
}

// using constructor function
function Person () {
    this.name = 'Sam'
}

let person1 = new Person();
let person2 = new Person();

• Each object created from the constructor function is unique. You can have the same properties as the constructor function or add a new property to one particular object. For example,

// using constructor function
function Person () {
    this.name = 'Sam'
}

let person1 = new Person();
let person2 = new Person();

// adding new property to person1
person1.age = 20;

Now this age property is unique to person1 object and is not available to person2 object.

However, if an object is created with an object literal, and if a variable is defined with that object value, any changes in variable value will change the original object. For example,

// using object lateral
let person = {
    name: 'Sam'
}

console.log(person.name); // Sam

let student = person;

// changes the property of an object
student.name = 'John';

// changes the origins object property
console.log(person.name); // John

When an object is created with an object literal, any object variable derived from that object will act as a clone of the original object. Hence, any change you make in one object will also reflect in the other object.

Adding Properties And Methods in an Object

You can add properties or methods in an object like this:

// constructor function
function Person () {
    this.name = 'John',
    this.age = 23
}

// creating objects
let person1 = new Person();
let person2 = new Person();

// adding property to person1 object
person1.gender = 'male';

// adding method to person1 object
person1.greet = function () {
    console.log('hello');
}

person1.greet();   // hello

// Error code
// person2 doesn't have greet() method
person2.greet();

Output

hello
Uncaught TypeError: person2.greet is not a function

In the above example, a new property gender and a new method greet() is added to the person1 object.

However, this new property and method is only added to person1. You cannot access gender or greet() from person2. Hence the program gives error when we try to access person2.greet();

JavaScript Object Prototype

You can also add properties and methods to a constructor function using a prototype. For example,

// constructor function
function Person () {
    this.name = 'John',
    this.age = 23
}

// creating objects
let person1 = new Person();
let person2 = new Person();

// adding new property to constructor function
Person.prototype.gender = 'Male';

console.log(person1.gender); // Male
console.log(person2.gender); // Male

JavaScript Built-in Constructors

JavaScript also has built-in constructors. Some of them are:

let a = new Object();    // A new Object object
let b = new String();    // A new String object
let c = new Number();    // A new Number object
let d = new Boolean();   // A new Boolean object

In JavaScript, strings can be created as objects by:

const name = new String ('John');
console.log(name); // "John"

In JavaScript, numbers can be created as objects by:

const number = new Number (57);
console.log(number); // 57

In JavaScript, booleans can be created as objects by:

const count = new Boolean(true);
console.log(count); // true

Note: It is recommended to use primitive data types and create them in a normal way, such as const name = 'John';, const number = 57; and const count = true;

You should not declare strings, numbers, and boolean values as objects because they slow down the program.

#javascript #programming 

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JavaScript Constructor Functions. IN JUST 6 MINUTES!!!

JavaScript Constructor Functions made simple.

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#javascript #functions #constructor #constructor functions #javascript constructor functions

The Difference Between Regular Functions and Arrow Functions in JavaScript

Other then the syntactical differences. The main difference is the way the this keyword behaves? In an arrow function, the this keyword remains the same throughout the life-cycle of the function and is always bound to the value of this in the closest non-arrow parent function. Arrow functions can never be constructor functions so they can never be invoked with the new keyword. And they can never have duplicate named parameters like a regular function not using strict mode.

Here are a few code examples to show you some of the differences

this.name = "Bob";
const person = {

name: “Jon”,
<span style="color: #008000">// Regular function</span>
func1: <span style="color: #0000ff">function</span> () {
    console.log(<span style="color: #0000ff">this</span>);
},

<span style="color: #008000">// Arrow function</span>
func2: () =&gt; {
    console.log(<span style="color: #0000ff">this</span>);
}

}
person.func1(); // Call the Regular function

// Output: {name:“Jon”, func1:[Function: func1], func2:[Function: func2]}
person.func2(); // Call the Arrow function

// Output: {name:“Bob”}

The new keyword with an arrow function

const person = (name) => console.log("Your name is " + name);
const bob = new person("Bob");
// Uncaught TypeError: person is not a constructor

If you want to see a visual presentation on the differences, then you can see the video below:

#arrow functions #javascript #regular functions #arrow functions vs normal functions #difference between functions and arrow functions

Private Constructor in Java: Use Cases Explained with Example

Introduction

A private constructor in Java is used in restricting object creation. It is a special instance constructor used in static member-only classes. If a constructor is declared as private, then its objects are only accessible from within the declared class. You cannot access its objects from outside the constructor class.

Private Constructor Use-Cases

Private constructors in Java are accessed only from within the class. You cannot access a private constructor from any other class. If the object is yet not initialised, then you can write a public function to call the private instructor. If the object is already initialised, then you can only return the instance of that object. A private constructor in Java has the following use-cases:

• You can use it with static members-only classes.
• You can use it with static utility or constant classes.
• You can use it to serve singleton classes.
• You can use it to assign a name, for instance, creation by utilising factory methods.
• You can use it to prevent subclassing.

Singleton Class

The private constructor in Java is used to create a singleton class. A singleton class is a class in Java that limits the number of objects of the declared class to one. A private constructor in Java ensures that only one object is created at a time. It restricts the class instances within the declared class so that no class instance can be created outside the declared class. You can use the singleton class in networking and database connectivity concepts.

#full stack development #java #private constructor #private constructor java #private constructor in java: use cases explained with example #use cases explained with example

Function Expression vs Function Declaration in JavaScript

Function Expression vs Function Declaration in JavaScript.

It was until during one of the JavaScript mock interviews did I came across the term function expression.

The question was: What is the difference between these two syntax?

function x(){

}

let x = function(){

}

I was clueless for a moment. After thinking a little, I could only come up with: the second syntax invokes an _anonymous _function and is assigned to a variable.

I was alien to the term hoisting.

In this article, we will acquaint ourselves with three simple terms: function declaration,_ function expression, _and hoisting.

What is function declaration?

Function declaration is also known as _function statement. _It contains the name of the function, parameters, and a return statement. **Naming the function **is what sets function declaration apart. Parameters and return statement is optional.

Function Declaration

What is function expression?

Function expression also has a name, parameters, and return statement. All of which are optional. The important thing to bear in mind is: the function here is _assigned _to a JavaScript variable.

Function Expression

#function-expression #function-declaration #functions-in-javascript #coding #javascript #express

JavaScript Factory Functions

JavaScript factory functions made simple.

📺 The video in this post was made by Programming with Mosh
The origin of the article: https://www.youtube.com/watch?v=jpegXpQpb3o&list=PLTjRvDozrdlxEIuOBZkMAK5uiqp8rHUax&index=9
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