javascript – How to generate JsObject in Node.js c++ addon as fast as in pure js?

I am new as a Node.js cpp-addon developer, I need to return a very big Object from cpp(Node.js cpp-addon) to Javascript logic, here is my code:

cpp-addon case:

var addon = require('bindings')('addon.node')

console.time('perf');
console.log('This should be result:', addon.getBigObject('foo bar'));
console.timeEnd('perf');

#include <napi.h>

Napi::Value GetBigObject(const Napi::CallbackInfo& info) {
  Napi::Env m_env = info.Env();

  Napi::Object node = Napi::Object::New(m_env);
  node.Set(Napi::String::New(m_env, "foo"), Napi::Number::New(m_env, 1));
  node.Set(Napi::String::New(m_env, "body"), Napi::Array::New(m_env));


  for (int i = 0; i < 2000000; i++) {
    Napi::Object stmt = Napi::Object::New(m_env);
    stmt.Set(Napi::String::New(m_env, "foo"), Napi::Number::New(m_env, 1));
    Napi::Array body = node.Get("body").As<Napi::Array>();
    auto len = std::to_string(body.Length());
    body.Set(Napi::String::New(m_env, len), stmt);
  }


  return node;
}

Napi::Object Init(Napi::Env env, Napi::Object exports) {
  exports.Set(Napi::String::New(env, "getBigObject"), Napi::Function::New(env, GetBigObject));
  return exports;
}

NODE_API_MODULE(addon, Init)

Running this code time cost:

perf: 2.782s

pure-js case:

var addon = require('./addon.js');

console.time('perf');
console.log('This should be result:', addon.getBigObject('var foo = 1;'));
console.timeEnd('perf');

module.exports.getBigObject = function() {
  const node = {};
  node.foo = 1;
  node.body = [];
  for (let i = 0; i < 2000000; i++) {
    let body = node.body;
    body.push({
      foo: 1
    });
  }
  return node;
}

Running this code time cost:

perf: 220.973ms

Why is this so slow that generate JsObject in cpp-addon?