Use class-extends to wrap Pool

[NatalieWolfe]

Using the es5-style pool wrapping from before makes it difficult to subclass BoundPool. Since Node 4.5 is the lowest supported version, it is possible to use es6-style classes.

The subsclassing issue stems from the fact that BoundPool was not applying Pool to this, instead returning a new Pool instance. It couldn't safely apply Pool since Pool is an es6 class and you must call es6 class constructors with new. By changing BoundPool to also be an es6 class we can call super and thus "apply" the Pool constructor to this.

[charmander]

This is semver-major, though, since pg.Pool(…) will stop working without new. See #1505 (comment)

[brianc]

@NatalieWolfe thanks for your work on this...and I apologize for the delay. I'm going to bundle this up with [https://github.com//pull/1503] because I think that also requires semver major, right @charmander?

[charmander]

@brianc It depends on a pull request that should be a major version of pg-native, but I don’t think it needs to be a major version of pg. (The change to pg-native causes its client to emit error events in more situations, but the way it affects the pg wrapper can be considered a bugfix.)

[brianc]

@charmander I think you might have responded to the wrong pull request here w/ your comment? Because this removes the ability to do const pool = pg.Pool() (now requiring new) it's a subtle breaking change which unfortunately requres a semver major. Once the minor patches settle down a bit here I'll do the semver major bump for this.

[sehrope]

There's a bunch of stuff in node core that detects if it's not called as a constructor and if so silently returns the constructor invocation instead:

Here's an example from the zlib module:

function Gzip(opts) {
  if (!(this instanceof Gzip))
    return new Gzip(opts);
  Zlib.call(this, opts, GZIP);
}

Not sure if the rest of this PR would end up being semver major anyway but this approach might be something to consider to do this class changeover in a less intrusive way.

[NatalieWolfe]

@sehrope That only works for function based classes. When you use the ES6 class keyword, usage of new is enforced at the language level.

[sehrope]

Ah good point. Nevermind!

[charmander]

@brianc Sorry for the ambiguous wording; it =

I'm going to bundle this up with [https://github.com//pull/1503]

#1503 is a bugfix.