What is copy by value and copy by reference?

Before going to details about copy by value and copy by reference first, we need to know about Primitive datatype and non-primitive data type

What is a Primitive data type?

Primitive data types are :

-Number -Boolean -Undefined -String -Null

The non-primitive data types are:

Object Array

copy by Value:- When we pass Primitive data types we actually share value to the other data types. Let's see an example

let a=10;
let b=a;
b=20;

console.log(a) // 10
console.log(b) // 20

In the above example, we actually pass the value of a so change in b will not reflect in a.Same concept apply to all other primitive data types as well.Let's see an another example of copy by value

let str1 = "car";
let str2 = str1;
str2 = "truck";
console.log(str1) // car
console.log(str2) // truck

copy by reference:- In non-primitive data type we pass reference means address of a variable .Let's see an example

let person = {
  name: 'John',
  age: 25,
};

let newPerson=person;
newPerson.age=30;
console.log(person) // {name: 'John', age: 30}

here person.age value also changed because we pass address of person so newperson can access all the values of person and can manipulate also which will reflect on person also