ObjectWrap and JSON.stringify

[atoy40]

Hello,

I' like to know if it is possible to get something from a JSON.stringify() call on an "ObjectWraped" instance ?
Do I have to implement specific methods into my object code (i"ve try to implement getOwnPropertyNames and set property enumerable) ?

Anthony.

[NickNaso]

Hi @atoy40 ,
you coluld retrieve JSON.stringify from the global object like reported below:

// In your native function
Napi::Object json = env.Global().Get("JSON").As<Object>();
Napi::Function stringify = json.Get("stringify").As<Function>();

// Use stringify function
stringify.Call(json, { /*your json object*/ }).As<String>();

Hope to be helpful.

[atoy40]

@NickNaso thanks, but that's not what i'm searching for :)
My problem is this : I've a c++ object wrapped into a node object through ObjectWrap. this object expose some acccessors. Then, in my javascript code, if I try JSON.stringify(an_instance_of_myobject);, i only get MyObject {}

The question, is it possible to get properties of my object into the json return value ?.

[NickNaso]

@atoy40 Sorry I misunderstood your need. I try later to create an example for you. I will start from this example https://github.com/nodejs/node-addon-examples/blob/master/6_object_wrap/node-addon-api/myobject.cc
is it good for you?

[atoy40]

@NickNaso yes, I started from this kind of example to define my object, so it is looking like this one ... but with accessors instead of methods.

[atoy40]

@NickNaso I've found some results. By implementiing two functions : toJSON for the json stringify, and a function assigned to the symbol "nodejs.util.inspect.custom" for console.log display.

[DaAitch]

@atoy40 You need to go through the rules what JSON.stringify(...) is doing with the value parameter.
toJSON seems to be the first check so simply implement that function.

[sziraqui]

@atoy40 can you share your implementation of those two methods?

[vpaladino778]

Hi @atoy40 ,
you coluld retrieve JSON.stringify from the global object like reported below:

// In your native function
Napi::Object json = env.Global().Get("JSON").As<Object>();
Napi::Function stringify = json.Get("stringify").As<Function>();

// Use stringify function
stringify.Call(json, { /*your json object*/ }).As<String>();

Hope to be helpful.

Unrelated to this issue, but I had a question for @NickNaso

I'm trying to utilize your method here to converting a Napi::Object into a string containing json

void my JSFunc(const Napi::CallbackInfo& info) {
  Napi::Object myObject = info[0].As<Napi::Object>();

  Napi::Object json = env.Global().Get("JSON").As<Napi::Object>();
  Napi::Function jsonStringify = json.Get("parse").As<Napi::Function>();

  Napi::String stringValue = jsonStringify.Call(json, {myObject }).As<Napi::String>();

  cout << stringValue.Utf8Value();;
}

For some reason i'm receiving "FATAL ERROR: Error::New napi_get_last_error_info" as an error

[vpaladino778]

I was able to figure out my issue. For anyone else that comes across this, I realized this line:

Napi::Function jsonStringify = json.Get("parse").As<Napi::Function>();

Should have been:

Napi::Function jsonStringify = json.Get("stringify").As<Napi::Function>();

Silly mistake on my part, but just wanted to share.

[NickNaso]

Hi @vpaladino778,
I'm happy to see that you solved the problem. i prepared an example on which I illustrated the use of JSON.parse and JSON.stringify

#include <napi.h>

Napi::String JSONStringify(const Napi::CallbackInfo& info) {
  Napi::Env env = info.Env();
  Napi::Object json_object = info[0].As<Napi::Object>();
  Napi::Object json = env.Global().Get("JSON").As<Napi::Object>();
  Napi::Function stringify = json.Get("stringify").As<Napi::Function>();
  return stringify.Call(json, { json_object }).As<Napi::String>();
}

Napi::Object JSONParse(const Napi::CallbackInfo& info) {
  Napi::Env env = info.Env();
  Napi::String json_string = info[0].As<Napi::String>();
  Napi::Object json = env.Global().Get("JSON").As<Napi::Object>();
  Napi::Function parse = json.Get("parse").As<Napi::Function>();
  return parse.Call(json, { json_string }).As<Napi::Object>();
}

Napi::Object Init(Napi::Env env, Napi::Object exports) {
  exports["jsonStringify"] =  Napi::Function::New(env, JSONStringify);
  exports["jsonParse"] = Napi::Function::New(env, JSONParse);          
  return exports;
}

NODE_API_MODULE(json, Init)

'use strict'

const assert = require('assert')
const addon = require('bindings')('json');

const jsonObj = { a: 1 }
const jsonString = JSON.stringify(jsonObj)

assert.strictEqual(addon.jsonStringify(jsonObj), jsonString)
assert.deepStrictEqual(addon.jsonParse(jsonString), jsonObj)

I provide to attach the code complete code example.
json.zip

[vpaladino778]

@NickNaso

Hi Nick,

Thanks so much for this, it was helpful to me. It was very kind of you to take the time to put together this example.

[github-actions]

This issue is stale because it has been open many days with no activity. It will be closed soon unless the stale label is removed or a comment is made.

[mhdawson]

Going to close this as it looks like the discussion has run its course and the questions were answered. Please let us know if you think this was not the right thing to do.