JavaScript Objects

In JavaScript, objects are a fundamental data type that represent a collection of properties. A property is a key-value pair, where the key is a string (or symbol), and the value can be any data type.

Creating Objects

There are 4 ways to create objects:

1. Object literal notation

We're creating an object called person with three properties: name and age:

let person = {
    name: 'Paul',
    age: 30
};

2. Constructor function

A constructor function is a regular function that is called using the new keyword:

function Person(name, age) {
  this.name = name;
  this.age = age;
};

let person = new Person('Paul', 30);

3. Object.create()

The Object.create() method can be used to create an object with a specified prototype object and properties:

const personPrototype = {
    sayHello: function() {
        console.log(`Hello ${this.name}`);
    }
};

let person = Object.create(personPrototype, {
    name: { value: 'Paul' },
    age: { value: 30 }
});
person.sayHello(); // prints: Hello Paul

4. Class Notation

ES6 introduces classes that can be used to create objects. A class is a blueprint for creating objects with specific methods and properties:

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

let person = new Person('Paul', 30);

Accessing Properties

You can access an object's properties using dot notation or bracket notation:

let person = {
    name: 'Paul',
    age: 30,
    address: {
        city: 'London'
    }
};

console.log(person.name); // prints: Paul
console.log(person.address.city); // prints: London
console.log(person['age']); // prints: 30

In this example, we access the firstName property using dot notation and the lastName property using bracket notation.

Modifying Properties

You can modify an object's properties by assigning a new value to the property:

let person = {
    name: 'Paul',
    age: 30
};

person.age = 40;

console.log(person.age); // prints: 40

Adding Object Properties

You can add new properties to an object by assigning a value to a new key:

let person = {
    name: 'Paul',
    age: 30
};

person.twitter = '@90_10_dev';

console.log(person.twitter); // prints: @90_10_dev

In this example, we add a new property called twitter to the person object.

Take Away

Objects are used extensively in Javascript - they are incredibly flexible and powerful, and they can be used to represent a wide variety of data structures, including arrays, linked lists, trees, and graphs.