process.versions.modules is not for N-API ?

[linxiaowu66]

• Node.js Version: 13.2.0
• OS: Mac
• Scope (install, code, runtime, meta, other?): code
• Module (and version) (if relevant): N-API
  Hi guys, I have a problem about the global variable : process.versions.modules.

In the docs of nodejs, it describe the process.versions.modules as follow:

process.versions.modules indicates the current ABI version, which is increased whenever a C++ API changes. Node.js will refuse to load modules that were compiled against a different module ABI version.

So with this description, I think if I have a C++ addon with N-API build in the node v8(modules: '57'), and then use it the node v13(modules: '79'), it will throw error. But actually it does not.

And I read the nodejs source code, in the DLOpen function , I find this if statements:

// -1 is used for N-API modules
    if ((mp->nm_version != -1) && (mp->nm_version != NODE_MODULE_VERSION)) {}

as the comments, if this module is not N-API, so nodejs will compare the module version to current module version, if these two version is not the same, it will report error.

Now I am confusing with this code. versions.modules is not for N-API ?

Can anyone help me ?

Thanks.

[gireeshpunathil]

cc @nodejs/n-api

[NickNaso]

Hi @linxiaowu66,
if your native add-on is implemented using N-API you don't care of NODE_MODULE_VERSION, because your module will continue to work if you switch the Node.js version. What is important for N-API module is the N-API version. You can get the N-API version using process.versions (see: https://nodejs.org/dist/latest-v12.x/docs/api/process.html#process_process_versions) or you can use the napi_build_version (see: https://nodejs.org/dist/latest-v12.x/docs/api/process.html#process_process_config) in the binding.gyp.
N-API is an additive API and is versioned independently from Node.js so for example if you implement a native add-on with N-API v3 your module will work on all Node.js version that have N-API v3 or above. You can find information of wht N-API version is supported by different version of Node.js here https://nodejs.org/dist/latest-v12.x/docs/api/n-api.html#n_api_n_api_version_matrix
I hope that this help you

[linxiaowu66]

@NickNaso Firstly thanks for your answer.

Then I am still confusing. N-API is based on ABI version, and the ABI version can be found in the process.versions.modules, is it right ? If this is wrong, the description for process.versions.modules maybe misleading(https://nodejs.org/dist/latest-v12.x/docs/api/process.html#process_process_versions):

process.versions.modules indicates the current ABI version, which is increased whenever a C++ API changes. Node.js will refuse to load modules that were compiled against a different module ABI version.

Secondly, I am testing a N-API module, when i compile using v13.2.0(napi: v5), and run this module in the v8.12.0(napi: v3), But it still can run and nothing error, is it normal?

[legendecas]

N-API and Node.js C++ API offer different sets of API which have different ABI stabilities guarantees across Node.js versions.

N-API have its own ABI guarantees on N-API versions and is expected to be not related to Node.js versions. Its highest supported version in the Node.js could be retrieved by process.versions.napi. N-API offers merely C APIs which could be used in C++ too, and we have a nice C++ wrapper node-addon-api around it.

process.versions.modules indicates Node.js C++ Addon API versions, which doesn't offer guarantees on ABI stabilities across Node.js versions.

So for your questions:

Then I am still confusing. N-API is based on ABI version, and the ABI version can be found in the process.versions.modules, is it right ? If this is wrong, the description for process.versions.modules maybe misleading(https://nodejs.org/dist/latest-v12.x/docs/api/process.html#process_process_versions):

No, N-API version should be referred to process.versions.napi. process.versions.modules is for Node.js C++ API.

Secondly, I am testing a N-API module, when i compile using v13.2.0(napi: v5), and run this module in the v8.12.0(napi: v3), But it still can run and nothing error, is it normal?

Yes, it is expected behavior. And this is what nice things N-API offer 🎉.

[legendecas]

Secondly, I am testing a N-API module, when i compile using v13.2.0(napi: v5), and run this module in the v8.12.0(napi: v3), But it still can run and nothing error, is it normal?

Note that this would work only if you write your addon with N-API v3 and lower APIs, not higher.

[linxiaowu66]

@legendecas @NickNaso Thanks a lot.