Is it possible to use 2 factory functions to populate 1 instance?

Question

Using a single factory function to populate an instance is straightforward. In the example below I use the factory function aircraftFactory() to create a new instance called supermarine. However I'm not sure how to structure this so that both aircraftFactory() and engines() could be used together to create supermarine.

"use strict"

function aircraftFactory(x) {
    return {
        manufacturer: x.manufacturer,
        factory: x.factory
    }
}

function engines(x) {
    return {
        numberOfEngines: x.numberOfEngines,
        costPerEngine: x.costPerEngine
    }
}

let supermarine = aircraftFactory({manufacturer: 'Supermarine', factory: 'Southampton'});

document.querySelector('.output').textContent = supermarine.manufacturer;

<div class='output'></div>

I tried chaining them together like this but it threw an error.

Uncaught TypeError: aircraftFactory(...).engines is not a function

let supermarine = aircraftFactory({manufacturer: 'Supermarine', factory: 'Southampton'}).engines({numberOfEngines: 1, costPerEngine: 35000});

I know there must be a pattern but I can't find an example or figure it out. Thanks for any help!

You want to merge the two objects? you can add properties to JS literal objects just doing obj.property = x; The "dot notation" will try to call a property or method form the object. — desoares
– desoares, Commented Apr 28, 2018 at 2:21
I don't necessarily want to merge the factories. In some instances I may want to use 1 and other times both. So I need to keep them separate and call them as needed. I know how to add single properties but I'd rather do it with factories. — DR01D
– DR01D, Commented Apr 28, 2018 at 2:23
That's too unclear, why and when you would decide it? On creation? — desoares
– desoares, Commented Apr 28, 2018 at 2:25
Yes when I create the instance sometimes I may want to use 1 factory function, other times I may want to call multiple factory functions. — DR01D
– DR01D, Commented Apr 28, 2018 at 2:26

desoares · Accepted Answer · 2018-04-28 02:53:00Z

I think I have a suggestion for you:

function engines(x) {
    return {
        numberOfEngines: x.numberOfEngines,
        costPerEngine: x.costPerEngine
    }
}

If you pass an engine:

function aircraftFactory(x, engine) {
    let aircraft = {
        manufacturer: x.manufacturer,
        factory: x.factory
    };

    if (engine) {
      aircraft.numberOfEngines = engine.numberOfEngines;
      aircraft.costPerEngine = engine.costPerEngine;
    }

    return aircraft;
}

You could create an instance like this:

let aircraft = aicraftFactory(x, engineFactory(y));

But if you want to create the properties without knowing the names:

function aircraftFactory(x, extended) {
    let aircraft = {
        manufacturer: x.manufacturer,
        factory: x.factory
    };

    if (engine) {
        for (let key in extended) {
            aircraft[key] = extended[key];
        }
    }

    return aircraft;
}

John Velasquez · Accepted Answer · 2018-04-28 03:08:36Z

1

To extend engines to aircraftFactory you need to use prototype

Prototypes extends/inherit your properties and methods.

Try this

"use strict"

function aircraftFactory(x) {
  this.manufacturer = x.manufacturer;
  this.factory = x.factory;
}

function engines(x) {
    return {
        numberOfEngines: x.numberOfEngines,
        costPerEngine: x.costPerEngine
    }
}

//This is where you extend engines
aircraftFactory.prototype.engines = engines;

//Create the instance of aircraftFactory
let supermarine = new aircraftFactory({manufacturer: 'Supermarine', factory: 'Southampton'}).engines({numberOfEngines: 1, costPerEngine: 35000});

edited Apr 28, 2018 at 3:08

answered Apr 28, 2018 at 2:58

John Velasquez

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3 Comments

DR01D Over a year ago

Is there a way to encapsulate that into 1 instance instead of both supermarine and test?

DR01D Over a year ago

Very interesting. Your example used a constructor. It's not possible with a factory function?

John Velasquez Over a year ago

nope you can't, prototype needs new and constructor

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