perf(documentarray): refactor to use ES6 classes instead of mixins, 30% speedup

[vkarpov15]

Before:

$ time node gh-7895.js 

real	0m10.777s
user	0m11.311s
sys	0m0.354s

After:

$ time node gh-7895.js 

real	0m7.058s
user	0m7.194s
sys	0m0.048s

Should be fine to release in 5.6.8, but I want to see if we can make this a little bit faster, because this is still slightly slower than Mongoose 4.13

[vkarpov15]

It looks like I managed to fix the tests by removing event emitter registration in the doc array constructor - it isn't strictly necessary because we can just set isNew normally. However, this means I'd like to defer this change to 5.7.0. It shouldn't be backwards breaking, but it feels a little too risky for a patch release.

[brettkiefer]

This looks great! I found something kind of funny running our test suite against it that I thought I'd alert you to. I'm not sure if you'd consider it to be a bug in util.inspect, in this change, or neither.

If you run this script on 336e995 (with node 10 and 12, at least), you'll get infinite recursion in inspect's formatValue and ultimately RangeError: Maximum call stack size exceeded, whereas with e.g. 5.6.5, it would inspect the subdoc array as expected.

'use strict';

const mongoose = require('.');
const { inspect } = require('util');

const SubdocSchema = mongoose.Schema({ a: String, b: String, c: String, d: String, e: String  });
const Schema = mongoose.Schema({ name: String, subdocs: { type: [SubdocSchema] } });
const Model = mongoose.model('Test', Schema);
const data = { _id: new mongoose.Types.ObjectId(), name: 'test', subdocs: [{a: 'a'}] };
const model = new Model();
model.init(data);
console.log(inspect(model.subdocs));

That may be something you'd expect consumers to work around, but I thought it was worth calling out.

[vkarpov15]

Thanks @brettkiefer , I will look into this before merging

[brettkiefer]

To close the loop, f96a041 fixed the issue in our test suite that initially brought the infinite recursion issue up. Thank you!