Calling JavaScript from C++ with node.js

Question

Is there a way to call JS functions from C++ through node.js (as callbacks or something like that)? If yes, how? I\'m searching for it on the web, but haven\'t found any hel

Answer 1

One way to do it form a native addon can be using the provided function as a callback, for example let's gonna assume that you have a function named setPrintFunction() declared in your native environment (A native addon):

(Call this for example main.cc)

#include 
#include 

v8::Persistent fn;

// Call this at any time, but after the capture!
void printToNode(std::string msg) {
  auto isolate = fn->GetIsolate();
  // This part is the one that transforms your std::string to a javascript
  // string, and passes it as the first argument:
  const unsigned argc = 1;
  auto argv[argc] = {
      v8::String::NewFromUtf8(isolate,
                          msg.c_str(),
                          v8::NewStringType::kNormal).ToLocalChecked()
  };
  cb->Call(context, Null(isolate), argc, argv).ToLocalChecked();
}

// This is your native function that captures the reference
void setPrintFunction(const v8::FunctionCallbackInfo& args) {
  auto isolate = args.GetIsolate();
  auto context = isolate->GetCurrentContext();
  auto cb = v8::Local::Cast(args[0]);
  fn = v8::Persistent::New(cb);
}

// This part exports the function
void Init(v8::Local exports, v8::Local module) {
  NODE_SET_METHOD(module, "exports", setPrintFunction);
}

NODE_MODULE(NODE_GYP_MODULE_NAME, Init)

Then, just importing your addon and using it like:

(Call this for example index.js)

const { setPrintFunction } = require('');

function printNodeMsg(msg) {
  console.log(': ' + msg);
}

setPrintFunction(printNodeMsg);

So what you're basically doing is capturing the reference to the v8::Function (Which is the javascript function, but in the native environment) and then invoking it and passing "Hello World!" as the first (and unique) parameter.

More on the subject: https://nodejs.org/api/addons.html