Added support for Node 13

[giovannicalo]

As mentioned in #346, this library fails to install with Node 13.0.1, due to compilation errors.
After a quick investigation, the issue seems to be

v8::Local<v8::Value> v8::Object::Get(uint32_t index)

which has already been deprecated for a while and seems to have been removed in favour of

v8::MaybeLocal<v8::Value> v8::Object::Get(v8::Local<v8::Context> context, uint32_t index)

in Node 13 / V8 7.8.

This seems to fix the issue.

It's only been tested with Node 12.13.0 and 13.0.1, on Windows.

This might break compatibility with older versions of Node, however the new method was already present (and the old one was already deprecated) in Node 6 / V8 5.1, so it shouldn't be the case.

It might not be the best way to fix it, but works for me.

[lgeiger]

Thanks for the fix!

Could you add Node 13 to the list of node versions in travis.yml so we can test this fix on CI?

[lgeiger]

Thanks for adding it to travis.yml. I am not familiar with this part of the code and V8 in general, @reqshark @rolftimmermans could you take a quick look?

[rolftimmermans]

There is also the Nan::Get() helper which might be a safe alternative?

[giovannicalo]

As I said, there might be better ways to fix it.

I just needed it to work and figured I'd have a look, rather than downgrading Node, so I went with the least possible changes and stopped as soon as it worked.

Otherwise, lately I've been using node-addon-api rather than N-API, NAN or V8.

Anyway, I guess it's between

Local<Object> buf = batch->Get(Nan::GetCurrentContext(), i).ToLocalChecked().As<Object>();

and

Local<Object> buf = Nan::Get(batch, i).ToLocalChecked().As<Object>();

which is shorter and probably more stable, so might indeed be better.

[lgeiger]

@rolftimmermans What do you think, can we merge this, or should we use Nan::Get()?

I am not very familiar with this, but I can do a patch release once this PR is merged.

[rolftimmermans]

Let’s just merge for now, we can always improve later!

[lgeiger]

Let’s just merge for now, we can always improve later!

👍 @giovannicalo Thanks for the PR. Let's ship it