Know Everything about Objects in Javascript - Basics

As we know in Javascript there are two different datatypes - Primitive Datatype like string, number, boolean, undefined, null, Symbol(introduced in ES6) and Reference Datatype like object.
Primitive datatypes are immutable(cannot be changed) and values contain only a single thing (a string or a number etc) whereas Objects are mutable(can be changed).

What is Object?

An object is an unordered list of data types, stored as name-value(or key-value) pairs. Each item in the list is called a property (and functions are called methods).e.g.
let person = {name : "Alex",  age: 27 };
console.log(person); 
output:

1. {name: "Alex", age: 27}
1. age: 27
2. name: "Alex"
3. __proto__: Object
We can also create the same person object differently

let person = new Object();
person.name = "Alex";
person.age = 27;
console.log(person);
output:

1. {name: "Alex", age: 27}

Generally, property names are kept as string but it can be a string or a number.e.g.

let person = { name : "Alex", 34 : "age", "Year of graduation": 2014 };

1. {34: "age", name: "Alex"}

NOTE : If the property name is a number or string with space, it has to be accessed with the bracket notation.

Is object a Reference datatype?

An object, is a reference data type. Variables(e.g. person) that are assigned a reference value(means object) are given a reference or a pointer to the location in memory. The variables don’t actually store the value.This is the reason why objects are called reference datatype.
Also because of reference type, when a object is changed, all its referenced objects gets changed and vice-versa.e.g.
let person = { name : "Alex" , age : 27 };
let man = person;
console.log(man);

1. {name: "Alex", age: 27}

// Now if we change the property of man,it will change person object and vice-versa
man.name = "Chris";
console.log(man);

1. {name: "Chris", age: 27}

console.log(person);

1. {name: "Chris", age: 27}

Similarly if we change person,it will reflect in man also.

NOTE : To avoid this we can use spread operator introduced in ES - 6.

Creating object from another object

let person = { name : "Alex" , age : 27 };
let man = {...person};
Assign new property 
let lynda = {...person,sex : "female" };
Reassign value to existing property
let marrie = {...lynda, name : "Marrie"};

Accessing properties of object

The properties of an object can be accessed in two ways:

• Dot Notation
• Bracket Notation

Dot Notation is highly used to access the property value of object. We can use dot-notation to read/change or create a property of object.
let person = { name : "Alex" , age : 27 };
console.log(person.name); // Alex
person.name = "Alex Voucher";
If we try to access a property which doesn't exist for an object we get undefined value for it.
console.log(person.profession); // undefined
person.profession = "Engineering";
console.log(person);

1. {name: "Alex Voucher", age: 27, profession: "Engineering"}

The key or property name of object can be a string, number or string with spaces. In case of property name with single word can be accessed with dot-notation but property with number or string with space can be accessed with bracket-notation.
let person = { name : "Alex" , age : 27 , "year of birth" : 1990 , 3 : "graduation degree"};
console.log(person["name"]); // Alex
console.log(person["year of birth"]); // 1990
console.log(person[3]); // graduation degree
person["profession"] = "Engineering";
console.log(person);

1. {3: "graduation degree", name: "Alex", age: 27, year of birth: 1990, profession: "Engineering"}

Object as a property
let person = { name : "Alex" , age : 27 , 
                address : { 
                    city : "New Delhi", 
                    country : "India"}
             };
console.log(person.address.country); // India
Deleting a property
delete person.age;   // true
console.log(person.age); // undefined

So in this article we have covered the basics of Javascript object. Hope this article was helpful. Subscribe and leave your comments to support.
Thank you!!