How to make an inherited method private in extended class

Question

I want to make an inherited method private outside of the extended class in Typescript

Let's say I have two classes like this:

class BaseClass{
    constructor(){}

    sayHello(){
        console.log('hello');
    }
}

class Class extends BaseClass{
    constructor(){
        super();
    }

    private sayHello(){  //I don't want to have to do this every time
        super.sayHello(); 
    }
}

let obj = new Class();
obj.sayHello();

I need to access the method sayHello() inside of 'Class' but it shouldn't be accessible from outside. I don't want to have to overwrite it every time I inherit.

I don't think this is possible. also, it's a bad idea because it violates the Liskov Substitution Principle https://stackify.com/solid-design-liskov-substitution-principle/ — M.Elkady, Jul 04 '19 at 18:44
@M.Elkady it doesn't violate the Liskov Substitution Principle because using the accepted answer the method isn't accessible from outside in both cases (which is what I needed) and therefore doesn't change the behavior of the class — hkonsti, Jul 04 '19 at 20:09

Kevin Pastor · Answer 1 · 2023-01-13T22:42:36.907

3

The keyword protected makes the method accessible only to extended classes and not to the outside.

class BaseClass {
    constructor() { }

    protected sayHello() {
        console.log('hello');
    }
}

class Class extends BaseClass {
    constructor() {
        super();
    }

    protected sayHello() {
        super.sayHello(); 
    }
}

edited Jan 13 '23 at 22:42

answered Jul 04 '19 at 18:38

Kevin Pastor

761
3
18

score 1 · Accepted Answer · answered Jul 04 '19 at 18:37

I think you are looking for the protected access modifier. A protected member is accessible from derived classes but not from outside the class

class BaseClass{
    constructor(){}

    protected sayHello(){
        console.log('hello');
    }
}

class Class extends BaseClass{
    constructor(){
        super()
        this.sayHello() // ok
    }
}

let obj = new Class();
obj.sayHello(); //err

How to make an inherited method private in extended class

2 Answers2