ES6 javascript inheritance

Question

Provided the following code:

class Person {
    constructor(name) {
        this.name = name;
    }
    sayHello() {
        console.log('Hello, my name is ' + this.name);
    }
    sayHelloAndBy() {
        this.sayHello();
        console.log('Bye');
    }

}
class Student extends Person {
    constructor(name, grade) {
        super(name);
        this.grade = grade;
    }
    sayHello() {
        console.log(`Hi, I'm a studend and my name is ` + this.name);
    }
}


let b = new Student("Some guy", 5);

b.sayHelloAndBy();

I would like to figure out a way of calling sayHello as defined in Person and not in Student. Is it possible ?

In php there is the self:: which allows one to do this, but I'm not sure if JS has a similar concept.

Depends from where you want to call it. So, where do you want to call Person’s sayHello method ? — Felix Kling
– Felix Kling, Commented Oct 17, 2017 at 14:25
You can use super in methods to refer to an overridden parent method. — Jared Smith
– Jared Smith, Commented Oct 17, 2017 at 14:25
@Ryan That would change the context inside sayHello. this would point the child not the parent inside of sayHello. — Rajaprabhu Aravindasamy
– Rajaprabhu Aravindasamy, Commented Oct 17, 2017 at 14:27

Ry- · Accepted Answer · 2017-10-17 14:30:44Z

4

You can refer to the version of sayHello defined in Person through Person’s prototype property and call it with the requisite this using Function#call:

sayHelloAndBye() {
    Person.prototype.sayHello.call(this);
    console.log('Bye');
}

Runnable:

class Person {
    constructor(name) {
        this.name = name;
    }
    
    sayHello() {
        console.log('Hello, my name is ' + this.name);
    }
    
    sayHelloAndBye() {
        Person.prototype.sayHello.call(this);
        console.log('Bye');
    }
}

class Student extends Person {
    constructor(name, grade) {
        super(name);
        this.grade = grade;
    }
    sayHello() {
        console.log(`Hi, I'm a studend and my name is ` + this.name);
    }
}

let b = new Student("Some guy", 5);

b.sayHelloAndBye();

edited Oct 17, 2017 at 14:30

answered Oct 17, 2017 at 14:29

Ry-♦

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2 Comments

Cerbrus Over a year ago

I'm pretty sure this is what the OP is looking for.

Felix Kling Over a year ago

However, if that’s the desired behavior a cleaner approach might be to put the logic into a new method that’s not supposed to be overwritten. I.e. _sayHello() {...} sayHello() { this._sayHello();} sayHelloAndBy() { this._sayHello();...} (or simply define a function outside the class and call that one).

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