Value Type vs Reference Type

Value Types (Primitives)

1. Int
2. String
3. Boolean
4. Symbol
5. undefined
6. null

Reference Types (Objects)

1. Object
2. Function
3. Array

Is it a value or a reference(pointer?)

Value Types save values

let x = 10
let y = x
x = 20
console.log(y)
// 10

Reference Types save pointers

let x = {value:10}
let y = x
x.value = 20
console.log(y)
// {value:20}

scope : Value Types

let number = 10

function increase(number){
  number ++;
}

increase(number)
console.log(number)
//10

This is because the number value was copied into the function scope. It is independent.

scope: Reference Types

let number = {value:10}

function increase(number){
  number.value ++;
}

increase(number)
console.log(number)
//{value:11}

This is because number reference was copied into the function. It is the same. Objects are copied by their reference!