The **TypeScript accessor** provides us with a way to implement [encapsulation](https://www.educative.io/answers/how-to-use-encapsulation-in-java).

In simple terms, **`encapsulation`** hides the data members so that they can only be accessed by the member functions of the same class.

The code snippet below provides an example of `encapsulation`.

class User{
  firstname:string
  lastname:string

  fullName(){
    return this.firstname + " " + this.lastname
  }
}

let user1 = new User();

//setting the firstname and lastname from outside class
user1.firstname = "John"
user1.lastname = "Doe"

console.log(user1.fullName())

In the code above:

* Lines $1$ to $8$ define the `User` class, which contains `firstname` and `lastname` as member variables, and `fullname()` as a member function.

* Line $10$ creates an instance of the `User` class and stores it in the `user1` variable.
* Lines $13$ to $14$ set the values for member variables `firstname` and `lastname` from outside the class. 
  >We allow external changes to the data here, but sometimes we may not want to expose the data. In that case, we use the `encapsulation` concept.


# 
## Getter and setter
Typescript accessor provides two methods to perform get and set operations.
1. **`Getter`**: This method is used to retrieve a value and can be invoked through the `get` keyword.
2. **`Setter`**: This method is used to set a value and can be invoked through the `set` keyword.

We will modify the `User` class example above with `getter` and `setter`.


class User{
  private firstname:string
  private lastname:string

  set fname(f:string){
    this.firstname = f.toUpperCase();
  }

  set lname(f:string){
    this.lastname = f.toUpperCase();
  }

  get fullName(){
    return this.firstname + " " + this.lastname
  }
}

let user1 = new User();
user1.fname = "John";
user1.lname = "Doe"
console.log(user1.fullName)

The changes made to the code are as follows:

* In lines $2$ to $3$, the access type of the member variables is now `private`. 

* Lines $5$ to $15$ define two `setter` methods to set values for member variables. We can modify the data taken from the user in `setter` methods. Here, we convert names to uppercase. We also define a `getter` method to get `fullname`.
* Lines $19$ to $20$ use `setter` methods to set the values for member variables. We don't need to call the method here; instead, we can set values as variables.
* Line $21$ uses the `getter` method to print `fullname` to the console.

If we try to set values for `private` member variables, the TypeScript compiler will throw an error.

In the following code snippet, we try to set the value for the private member variable `firstname` in line $21$. The compiler will throw the ` Property 'firstname' is private and only accessible within class 'User'` error.

class User{
  private firstname:string
  private lastname:string

  set fname(f:string){
    this.firstname = f.toUpperCase();
  }

  set lname(f:string){
    this.lastname = f.toUpperCase();
  }

  get fullName(){
    return this.firstname + " " + this.lastname
  }
}

let user1 = new User();

//trying to set value "John" to private member variable firstname
user1.firstname = "John"

What is TypeScript accessor?

Getter and setter