With Node.js addons we can load our C++ libraries as if they were ordinary Node.js modules. The recommended way to implement these addons is using the N-API. The N-API is delivered as a part of the Node.js distribution. since v8 and became stable in v10.

One “Hello World” addon could look something like this:

// hello.cpp
#include <node.h>

namespace demo {

    using v8::FunctionCallbackInfo;
    using v8::Isolate;
    using v8::Local;
    using v8::Object;
    using v8::String;
    using v8::Value;

    void HelloWorld(const FunctionCallbackInfo<Value>& args) {
        Isolate* isolate = args.GetIsolate();
        args.GetReturnValue().Set(String::NewFromUtf8(isolate, "hello world").ToLocalChecked());
    }

    void Initialize(Local<Object> exports) {
        NODE_SET_METHOD(exports, "hello_world", HelloWorld);
    }

    NODE_MODULE(NODE_GYP_MODULE_NAME, Initialize)

}  // namespace demo

After building this code, we will get a hello_world.node file that is a dynamic library that wraps our HelloWorld function. Using require() in our JavaScript code we will import this C++ function to our Node.js application like this:

require('./path/to/hello_world.node');

Instead of loading this module directly we will use a helper module called node-bindings. This module checks all the possible locations that a native addon would be built at, and returns the first one that loads successfully. For example, if we built the debug version our native module will be located in the './build/Debug/addon' path, but if we compiled the debug version it will be in './build/Release/addon'. So, we will require our native module like this:

var addon = require('bindings')('addon_name')

Building the node modules

To compile our module we will use node-gyp, a tool written specifically to compile Node.js addons. This tool wraps gyp-next, a tool created by the Chromium team that starting from a script will generate project files for other build systems such as XCode projects, Visual Studio projects, Ninja build files, and Makefiles.

The input file for node-gyp is called binding.gyp and looks like this:

{
  "targets": [
    {
      "target_name": "hello_world",
      "sources": [ "hello.cpp" ]
    }
  ]
}

This file is telling node-gyp to compile generate a Makefile to compile hello.cpp and create a library that will be called hello_world.node. To create this Makefile do:

node-gyp configure

Now you could go to the build folder and run directly the project files generated to compile the node addon or do it using node-gyp:

node-gyp build

Using this module in our Node.js application should be as simple as:

// hello.js
const hello_module = require('bindings')('hello_world');
console.log(hello_module.hello_world());

Test this running node hello.js

You can find all the sources for this example in this github repository.