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 helpful resource.

Thanks in advance

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 <node.h> #include <string>  v8::Persistent<v8::Function> 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<Value>& args) {   auto isolate = args.GetIsolate();   auto context = isolate->GetCurrentContext();   auto cb = v8::Local<v8::Function>::Cast(args[0]);   fn = v8::Persistent<v8::Function>::New(cb); }  // This part exports the function void Init(v8::Local<v8::Object> exports, v8::Local<v8::Object> 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('<your path to .node file>');  function printNodeMsg(msg) {   console.log('<msg>: ' + 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