Javascript Object

What are JavaScript Objects?

• Objects are variables that can store both values and functions.
• Values are stored as key:value pairs called properties.
• Functions are stored as key:function() pairs called methods.

const students = {
  name:"abc",
  age:18,
  dept:"cs"
};

Object Properties

• Properties are key:value Pairs.
• A JavaScript object is a collection of properties.
• Properties can be changed, added, and deleted.

Access Properties

• Dot notation
• Bracket notation
• Expression

// objectName.property
let age = students.age;

//objectName["property"]
let age = students["age"];

//objectName[expression]
let age = students[x];

Changing Properties

You can change the value of a property:

const person = {
  name: "vijay",
  age :  50
};
person.age = 10;
console.log(person.age);


output:
10

Add New Properties

You can add a new property by simply giving it a value.

const person = {
  name: "vijay",
  age: 50
};
person.nationality = "English";
console.log(person.nationality);

output:
English

Delete Properties

The delete keyword deletes a property from an object.

const person = {
  name: "vijay",
  age: 50
};
delete person.age;
console.log(person);

output:
vijay

The delete keyword deletes both the value and the property.
After deleting, the property is removed. Accessing it will return undefined.

Nested Objects

Property values in an object can be other objects.

const students = {
  name:"abc",
  age:18,
  subject:{
      sub1:"cs",
      sub2:"maths",
      sub3:"cc"
}
};
console.log(students.subject.sub2;);

output:
maths

Object Methods

Methods are actions that can be performed on objects. Methods are functions stored as property values.

const students = {
  name:"abc",
  age:18,
  fullName: function() {
    return students.name + " " + students.age;
  }
};
let full=students.fullName();
console.log(full);

Object Constructors

Sometimes we need to create many objects of the same type. To create an object type we use an object constructor function. It is considered good practice to name constructor functions with an upper-case first letter.

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

}

// Create a Person object
const myFather = new Person("vijay", 50);
const myMother = new Person("thi", 45);
console.log(myFather);
console.log(myMother);