README.md

Proposal: Object.compose (composed prototypal Inheritance)

It is known that Object.assign is not suitable for Prototype Composition. By design, which I had to learn the hard way. I tried to do this:

import EventMachine from './libs/event-machine';


function RtcData( id ){
    const self = this;

    self._id = id;
    
    // ...

    EventMachine.call( self );
    
    // ...
}

// (!!!) NOTE: 'assign' does not work, the proposed 'compose' would
Object.assign( RtcData.prototype, EventMachine.prototype, {
   
    constructor: RtcData,
    
    get id(){
        const self = this;
        const prefix = 'fasel';
        return `${ prefix }-${ self._id }`;
    },
    
    send( /* args */ ){
        // this is a regular enumerable function
    },    
    ...
});



// the following log statements print 'undefined' or throw, instead of 'fasel-foobar', 
// because getter and setter methods won't get copied over by the 'assign' function

const rtData = new RtData( 'foobar' );
console.log( rtData.id ); 

rtData.on( 'someEvent', function( e ) {
    const rtDataContext = this;
    console.log( rtDataContext.id ); 
});

(Note: this example code originates in this project)

This behaviour is intended in JavaScript. During my research regarding this 'issue', I discovered the proposal for
Object.getOwnPropertyDescriptors scheduled to be released in the 2017th version of ECMAScript. At the bottom of the README.md the author outlines an example which takes Object.getOwnPropertyDescriptors a step further and enables exactly the behaviour I was looking for - a 'fixed' version of Object.assign.

Why?

• all the behaviour of inheritance that got syntax-sugared by the introduction of class in ES6 can be accomplished in a composing and more transparent and explicit way with Object.compose
• provides a fully working way of merging not only object instances but complete prototypes, which, at the end of the day, is still what's powering classes under the hood.

Implementation:

A working polyfill can be found here. Please note that I did not wrote this code, I just assembled it. The actual author is the one who proposed Object.getOwnPropertyDescriptors.