v8/node deprecated APIs and how to handle them

[chjj]

Putting this here to document for my own sanity.

V8 removed a bunch of calls and the node.js devs have decided to maintain them for the time being, but have marked them as deprecated. We need to switch away from them.

Deprecated APIs:

• Uint32Value()
• Int32Value()
• IntegerValue()
• NumberValue()
• BooleanValue()
• ToString()

Example migration:

Originally:

int32_t arg = info[0]->Int32Value();

Now must be:

int32_t arg = info[0]->Int32Value(Nan::GetCurrentContext()).FromJust();

Or:

int32_t arg = info[0]->Int32Value(Nan::GetCurrentContext()).ToChecked();

Or:

int32_t arg = info[0]->ToInt32(Nan::GetCurrentContext()).ToLocalChecked()->Value();

Int32Value returns Maybe<uint32_t>.

ToInt32 returns MaybeLocal<Int32>.

Note that ToChecked() is an alias for FromJust().

ToString() was also deprecated, but nan.h should be handling this. Not us, but for completeness, heres the migration.

From:

v8::Local<v8::String> str = info[0]->ToString();

To:

v8::Local<v8::String> str = info[0]->ToString(Nan::GetCurrentContext()).FromMaybe(v8::Local<v8::String>());

Note that anything that returns MaybeLocal instead of Maybe should have an IsEmpty() check.

Example (from the style guide below):

v8::MaybeLocal<v8::Value> maybe = fn->Call(...);

if (maybe.IsEmpty()) { // Exception occurs during function call
  // Do some clean up
  return; // Back to JavaScript and let it throw
}

v8::Local<v8::Value> result = maybe.ToLocalChecked();

References:

• Value Class:
  https://v8docs.nodesource.com/node-10.6/dc/d0a/classv8_1_1_value.html
• Int32 Class:
  https://v8docs.nodesource.com/node-10.6/de/da6/classv8_1_1_int32.html
• Maybe Class:
  https://v8docs.nodesource.com/node-10.6/d9/d4b/classv8_1_1_maybe.html
• MaybeLocal Class:
  https://v8docs.nodesource.com/node-10.6/d8/d7d/classv8_1_1_maybe_local.html
• Maybe Code: https://v8docs.nodesource.com/node-10.6/d4/da0/v8_8h_source.html
• v8.h (after the deprecation):
  https://github.com/addaleax/node/blob/78b888c6b1ca11e578be007a79476a792f726532/deps/v8/include/v8.h
• v8.h (master):
  https://github.com/nodejs/node/blob/master/deps/v8/include/v8.h

Timeline:

• Node Devs talk about the old APIs being removed (Sep. 27th):
  APIs removed in V8 7.0 and native addons nodejs/node#23122
• Node Devs decide to maintain old APIs but deprecate them (Sep. 28th):
  [v10.x] deps: increase V8 deprecation levels nodejs/node#23159

Style Guide (mentioning the changes):

• https://github.com/joyeecheung/node/blob/v8-maybe-doc/CPP_STYLE_GUIDE.md#use-maybe-version-of-v8-apis

I'm not sure how this will impact node versions prior to node v10. This maybe needs to be added as a part of nan? Not sure. Going to do more research.

Update:

Just discovered the magic of Nan::To (1, 2, 3).

We can do Nan::To<int32_t>(info[0]).FromJust().

Nan::To seems undocumented, but it seems to be the inverse of Nan::New.

[chjj]

It looks like nan has upgraded for this, but only for strings: nodejs/nan@24a22c3

Corresponding PR: nodejs/nan#808

Nevermind, looks like it's still in the works: nodejs/nan#811

[chjj]

Finally fixed with 3a3bb28

[chjj]

This issue seems to be getting a lot of attention from people in the community. Please note that Nan::To can be used in place of the nasty v8 syntax.

For example:

Nan::To<int32_t>(info[0]).FromJust()

Instead of:

info[0]->Int32Value(Nan::GetCurrentContext()).FromJust();