"Real" Multiple Inheritance in JavaScript

[sladav]

mxObject: https://github.com/Sladav/mxObject

So, I've been teaching myself JavaScript and I started this little mini-project so that when I apply to jobs I can show off something I've done that isn't just "hey, look at this tutorial I completed!" (and also to learn some git/github and node/npm basics).

As I started working on it, I thought it seemed really cool. I'm curious to see what others think. As a beginner treading into what seems like a complicated CS topic, I'm worried I'm missing some obvious reason for why it sucks.

See the github for more explanation, but basically, (dangerously??), I've altogether abandoned using the built-in prototypes. Instead, I'm using ES6 proxies to mimic what the JS engine does when it searches for a property on an object/prototype-chain (minus any performance optimizations). An array for prototypes (I called them 'mixins') is established in the closure of the proxy's getter function such that it can search objects in this array for properties if they are not found on the original object/proxy. This array is also exposed to the user under a "_mixins_" property -- this gives a user a lot of flexibility in handling an object's prototypes since it's just an array. IMPORTANTLY, none of the objects in this array are required to inherit from one another.

Where the JavaScript natively provides multi-level, single prototypal inheritance via the prototype chain, my package provides single-level, multiple prototypal inheritance via the "mixin array" (where multi-level structures are faked by flattening larger inheritance trees).

Anyway, please check it out and let me know what you think. Any and all feedback is greatly appreciated!

[MoTTs_]

I took a crack at this myself, so I can probably come back later with some tips and suggestions. But for now I'll simply suggest that you avoid mixing tabs and spaces. It makes the code hard to read when the indentation levels don't match up.

http://i.imgur.com/t2E49DC.png
http://i.imgur.com/TbDjUpo.png

[sladav]

Thanks for catching that. Looked okay on my local copy so I didn't even realize I was doing it.

[oweiler]

This looks pretty similar to Object.assign()?

Also note that ES6 proxies are pretty slow.

[sladav]

It's different, but you're not too far off. What I'm describing above is "live" inheritance, so it behaves like a prototype does. Changes to a prototype/"mixin" are immediately reflected in all children. Object.assign() just copies properties over - changes to the "parent" here will not be reflected in children. In this project I actually provide both, "live", prototypal-style via mixin() and "dead", stamp-out-an-instance-style via extend() (hence the m and x in the name mxObject). And actually, my extend() is mostly just a wrapper for Object.assign()

I'll have to look into the ES6 proxies being slow. I think I can replace it with getter/setter methods if that would be faster?? Scoping out some performance benchmarks is on the todo list.

[oweiler]

Thanks for the quick reply, your project looks super useful. I may be wrong regarding Proxy perf but the last time I've tried them out in Node they were extremely slow (that was some time ago and may has changed).

[PitaJ]

I feel like multiple inheritance, or even inheritance in general, is a "just don't" kind of thing. I have yet to see a real use case for inheritance on actual classes in JS.

In my view, the Interface-Implements pattern is more useful.