CLR class with toJSON method throws a "JavaScriptException: No public methods with the specified arguments were found" error on JSON.stringify

[kxs-rgamezdiaz]

I am using Jint 4.6.0.0 and need to add a toJSON method explicitly, which causes a "No public methods with the specified arguments were found" error.

Example:

public sealed class MyClassToJson()
{
    public string toJSON() => "{ \"name\": \"MyClassToJson\" }";
}

[TestMethod]
public void TestToJson() // Passes
{
    Jint.Engine engine = new();
    MyClassToJson myClass = new();
    engine.SetValue("myClass", myClass);
    string result = engine.Evaluate("myClass.toJSON()").ToString();
    Assert.AreEqual(myClass.toJSON(), result);
}

[TestMethod]
public void TestJsonStringify() // Fails
{
    Jint.Engine engine = new();
    MyClassToJson myClass = new();
    engine.SetValue("myClass", myClass);
    string result = engine.Evaluate("JSON.stringify(myClass)").ToString();
    Assert.AreEqual(myClass.toJSON(), result);
}

The TestJsonStringify test fails with this stacktrace:

Message: 
Test method ServerAPI.UnitTest.ScriptRuntimeV2.JintTests.TestJsonStringify threw exception: 
Jint.Runtime.JavaScriptException: No public methods with the specified arguments were found. ---> 
Jint.Runtime.JavaScriptException+JavaScriptErrorWrapperException: No public methods with the specified arguments were found.

  Stack Trace: 
stringify (<anonymous>:1:16)
<anonymous>:1:1
--- End of inner exception stack trace ---
Engine.ScriptEvaluation(ScriptRecord scriptRecord, ParserOptions parserOptions)
Engine.ExecuteWithConstraints[T](Boolean strict, Func`1 callback)
Engine.Execute(Prepared`1& preparedScript)
Engine.Evaluate(String code, String source)
JintTests.TestJsonStringify() line 55

Is this a bug or limitation in Jint? Is there a workaround? I need to have a toJSON method on my js class. Thank you for your help.

[kxs-rgamezdiaz]

Looks like I found a workaround, we need to return an ObjectInstance for the toJSON method.

public sealed class PersonWithToJsonJsValue(Jint.Engine engine)
{
    public string name { get; set; }
    public int age { get; set; }
    public ObjectInstance toJSON(JsValue v)
    {
        ObjectInstance obj = engine.Intrinsics.Object.Construct([]);
        obj.Set("name", name);
        obj.Set("age", age);
        return obj;
    }
}

[TestMethod]
public void TestJsonStringifyWithObjectWithToJsonReturningJsValue()
{
    Jint.Engine engine = new();
    PersonWithToJsonJsValue person = new(engine) { name = "John", age = 30 };
    engine.SetValue("person", person);
    string result = engine.Evaluate("JSON.stringify(person)").ToString();
    Assert.AreEqual("{\"name\":\"John\",\"age\":30}", result);
}

I will mark this an answer and change it later someone finds out how to do better.