Bdtjtk

I try to find out, if the current derived class has a property setter. Reason is that I loop a couple of options through the constructors of extended classes. and just want to assign those properties, that are part of this class and not the base class.

So I need a possibility to find out, if the getter or setter exist for this class or not. I remove as much code as possible to show case the issue only.

This is the base class:

class baseClass{

    constructor(wOptions){

        //do some stuff

        if(typeof wOptions == "object"){

            for(let prop in wOptions){

                // if(Object.getOwnPropertyDescriptor(this, prop) != undefined){

                // if(this.hasOwnProperty(prop) != undefined){ /* doesn't work either */

                if(typeof this[prop] != "undefined"){ /* calls the getter, if exists.  */

                    this[prop] = wOptions[prop];

                    delete wOptions[prop];

                } 

            }

        }       

    }

    get mainProperty(){

        return 42;

    }

    set mainProperty(newValue){

        return 42;

    }

}

Here is the the derived class:

class derivatedClass extends baseClass{

    constructor(wOptions){

        super(wOptions)

        //do some other stuff 

        let html = document.body;

        Object.defineProperty(this, "html", {value: html, writable: false});



        if(typeof wOptions == "object"){

            for(let prop in wOptions){

                // if(Object.getOwnPropertyDescriptor(this, prop) != undefined){

                // if(this.hasOwnProperty(prop) != undefined){ /* doesn't work either */

                if(typeof this[prop] != "undefined"){ /* calls the getter, if exists.  */

                    this[prop] = wOptions[prop];

                    delete wOptions[prop];

                } 

            }

        }       

    }

    get otherProperty(){

        return html.innerText;

    }

    set otherProperty(newValue){

        return html.innerText = newValue;

    }

}

And how to initialize the object:

let options = {otherProperty: "new Text"};

let object = new derivatedClass(options);

console.log(options);

Regarding the solutions tried already:

• 
  getOwnPropertyDescriptor always returns undefined; returns the options as assigned


• 
  hasOwnProperty always returns false ; returns the options as assigned


• 
  typeof this[prop] != "undefined" calls the getter and this can be pretty bad, because html is not defined yet. Reference Error for html.innerText
  


• Not a solution, but for verification: Removing the if clause in the derived class, changes the body text to new Text and prints an empty object in the console.

Tested in Chrome 71.

There would be some options to avoid this:

• shift all properties handled by this class to another object (pretty ugly and high possibility to forget a property in the list)


• use always Object.defineProperty, because they will be executed after the super call. However, it is not that pretty than the get/set functions of the class construct.

Is there any possibility to find out if there is a setter available for otherProperty, that evaluates true in the derivatedClass but not in the baseClass?

Try this one

const descriptor = Object.getOwnPropertyDescriptor(derivatedClass.prototype, 'otherProperty');

console.log(descriptor);

If derivatedClass.prototype has an otherProperty (otherwise returns undefined), it will return an object that contains some values. In the returned object, you should see get and set

More info here