A wrapper for a C++ class exposed in JavaScript

s2_cell_id_wrapper.cc

/* s2cellid.h */
#include <napi.h>
#include "s2/s2latlng.h"

class LatLng : public Napi::ObjectWrap<LatLng> {

  public:
    LatLng(const Napi::CallbackInfo& info);
    static Napi::FunctionReference constructor;
    static Napi::Object Init(Napi::Env env, Napi::Object exports);

  private:
    Napi::Value ToString(const Napi::CallbackInfo &info);
    S2LatLng s2latlng;
  
};

/* 
 * s2cellid.cc 
 * 
 * Usage in JavaScript:
 *   const s2 = require('@radarlabs/s2');
 *   const ll = new s2.LatLng(48.8584, 2.2945);
 *   ll.toString();  // "48.8584,2.2945"
 */

#include "latlng.h"

Napi::FunctionReference LatLng::constructor;

Napi::Object LatLng::Init(Napi::Env env, Napi::Object exports) {
  Napi::HandleScope scope(env);

  Napi::Function func = DefineClass(env, "LatLng", {
    InstanceMethod("toString", &LatLng::ToString)
  });

  constructor = Napi::Persistent(func);
  constructor.SuppressDestruct();

  exports.Set("LatLng", func);
  return exports;
}

LatLng::LatLng(const Napi::CallbackInfo& info) : Napi::ObjectWrap<LatLng>(info) {
  Napi::Env env = info.Env();
  Napi::HandleScope scope(env);

  int length = info.Length();
  if (length <= 0 || !info[0].IsNumber() || !info[1].IsNumber()) {
    Napi::TypeError::New(env, "(lat: number, lng: number) expected.").ThrowAsJavaScriptException();
    return;
  }

  Napi::Number lat = info[0].As<Napi::Number>();
  Napi::Number lng = info[1].As<Napi::Number>();

  this->s2latlng = S2LatLng::FromDegrees(
    lat.DoubleValue(),
    lng.DoubleValue()
  );
}

Napi::Value LatLng::ToString(const Napi::CallbackInfo& info) {
  return Napi::String::New(info.Env(), this->s2latlng.ToStringInDegrees());
}