binding.cc

#include <assert.h>
#include <stdio.h>
#include <node_api.h>

static napi_value AcceptTypedArray(napi_env env, napi_callback_info info) {
  napi_value typed_array = nullptr;
  size_t argc = 1;
  assert(napi_get_cb_info(env,
                          info,
                          &argc,
                          &typed_array,
                          nullptr,
                          nullptr) == napi_ok);
  bool is_typedarray = false;
  assert(napi_is_typedarray(env, typed_array, &is_typedarray) == napi_ok);
  assert(is_typedarray);
  napi_value arraybuffer = nullptr;
  napi_typedarray_type typed_array_type;
  size_t length = 0;
  void* data;
  assert(napi_get_typedarray_info(env,
                                  typed_array,
                                  &typed_array_type,
                                  &length,
                                  &data,
                                  &arraybuffer,
                                  nullptr) == napi_ok);
  fprintf(stderr,
          "type: %d\nlength: %lu\ndata: %p\n",
          typed_array_type,
          length,
          data);
  bool is_arraybuffer;
  assert(napi_is_arraybuffer(env, arraybuffer, &is_arraybuffer) == napi_ok);
  fprintf(stderr,
      "backing store is arraybuffer: %s\n", is_arraybuffer ? "true" : "false");
  fprintf(stderr, "value: %lf\n", *((double*)(data)));
  *((double*)(data)) *= 2;
  return nullptr;
}

NAPI_MODULE_INIT() {
  napi_value result;
  assert(napi_create_function(env,
                              "acceptTypedArray",
                              NAPI_AUTO_LENGTH,
                              AcceptTypedArray,
                              nullptr,
                              &result) == napi_ok);

  return result;
}

index.js

const acceptTypedArray = require('./build/Release/binding')

const buffer = new ArrayBuffer(8);
const array = new Float64Array(buffer);
array[0] = Math.PI;
acceptTypedArray(array);
console.log(array[0]);

const sharedBuffer = new SharedArrayBuffer(8);
const sharedArray = new Float64Array(sharedBuffer);
array[0] = Math.PI;
acceptTypedArray(sharedArray);
console.log(sharedArray[0]);