Export errors to allow typed access to them

[brandur]

Exports the errors module and the types it contains as stripe.errors.
This allows users to match on an error with the instanceof operator
instead of having to match on the string generated by accessing an
object's type.

There's a bit of an unfortunate singular/plural mismatch (the file is called
Error.js), but I called the export stripe.errors to match the
already-plural stripe.webhooks.

Fixes #457.

r? @jlomas-stripe Hey! Could I get your opinion on this?
cc @stripe/api-libraries

[brandur-stripe]

(And oops — I meant @jlomas-stripe. Sorry @JLomas!)

[jlomas-stripe]

@brandur-stripe This looks great. It looks like Error.js is only referenced in 3 places:

lib/StripeResource.js
lib/Webhooks.js
test/Error.spec.js

...so maybe we should also take this opportunity rename the file to Errors.js as well? Though ... it should still export Error, so maybe not. ¯\_(ツ)_/¯

Either way,

lgtm

[brandur-stripe]

...so maybe we should also take this opportunity rename the file to Errors.js as well? Though ... it should still export Error, so maybe not. ¯_(ツ)_/¯

Yeah, that's basically what stopped me. I think this would still be a good cleanup, but we should also rename the symbol Error to Errors too, and that would've added quite a bit of noise to this PR.

I'll merge this and then see if that tweak works the way we hope on a different PR. Thanks for taking a look!

[brandur-stripe]

Alright, I tried to follow this up with a rename, but it turned into quite a deep rabbit hole that I wasn't prepared for. Error.js seems to be doing something to manipulate the base Error that I don't understand, and a simple rename will cause a failure on this check:

  it('Populates with type and message params', function() {
    var e = new Error('FooError', 'Foo happened');
    expect(e).to.have.property('type', 'FooError');

It also has the additional problem that the author conflated a class with a package, and throughout much of the file, the singular _Error is more conceptually correct.

I'm just going to leave it for now.

[SimonSchick]

Little bit late here but, why are the errors exported on the client rather than directly from the package, this seems a little counter intuitive since errors are not bound to a stripe instance.

[jlomas-stripe]

@SimonSchick What do you mean? What would you expect to be able to do here? Like, const StripeErrors = require('stripe/lib/Error'); works just fine, but I'm not sure you'd ever do that since they're specific to Stripe...?