Fix CLR toJSON method invocation in JSON.stringify

[Copilot]

CLR classes with toJSON methods threw "No public methods with the specified arguments were found" when serialized via JSON.stringify. JSON.stringify calls toJSON() with no arguments, but the CLR method was exposed as MethodInfoFunction which failed to match the signature.

Changes

• TypeDescriptor: Detects public parameterless toJSON instance methods during type analysis
• ObjectWrapper: Wraps detected toJSON as ClrFunction in constructor, following the same pattern as length/dispose special properties
• Property flags: writable, configurable, non-enumerable (matches Date.prototype.toJSON behavior)

Example

public class MyData
{
    public string Name { get; set; }
    public int Value { get; set; }
    
    public object toJSON()
    {
        return new { name = Name, value = Value };
    }
}

var engine = new Engine();
engine.SetValue("data", new MyData { Name = "test", Value = 42 });

// Previously threw exception, now works:
engine.Evaluate("JSON.stringify(data)"); // {"name":"test","value":42}

Original prompt

---

This section details on the original issue you should resolve

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

Discussed in #2290

^{Originally posted by kxs-rgamezdiaz February 16, 2026}
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.

</issue_description>

<agent_instructions>Our TypeDescriptor should contain information whether type knows how to create toJSON description and it should be integrated the same way as ObjectWrapper already adds supported features based on object's shape.</agent_instructions>

Comments on the Issue (you are @copilot in this section)

• Fixes CLR class with toJSON method throws a "JavaScriptException: No public methods with the specified arguments were found" error on JSON.stringify #2291

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