System.InvalidCastException: 'Object must implement IConvertible.' when invoking callback function with object return value

[jsiemensLatitudegeo]

Version used

Tried both 2.11.58 and 3.0.0-beta-204.

Describe the bug

I'm trying to implement a function that returns a value, and when the value is an object, I get an InvalidCastException.

To Reproduce

    [Fact]
    public void TestJint2()
    {
        var flatMap = (IEnumerable<object> list, Func<object, int, IEnumerable<object>, object> callback) =>
        {
            int i = 0;
            return list.SelectMany(x =>
            {
                var intermediate = callback(x, i++, list);
                if (intermediate is IEnumerable enumerable)
                {
                    return enumerable.OfType<object>();
                }

                return new[] { intermediate };
            }).ToArray();
        };

        var engine = new Jint.Engine()
            .SetValue("flatMap", flatMap)
            .Execute(
                    @"var items = flatMap([1, [2, 3]], function(x) { 
                        return x; 
                    });");
    }

Expected behavior

The callback function is called, and the object is returned.

Additional context

When the callback is called with a primitive value like an integer, and an integer is returned, it works fine. It fails for reference types like arrays.

I was trying to implement the JavaScript flatMap method:
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/flatMap

[lahma]

I think that your flatMap signature is just too complex for Jint to handle. There are a lot samples which kind of signatures will work in InteropTests*.cs in the repo, maybe you could adapt something from there.

Generally if you want to implement JavaScript functionality, the signature should be JsValue FlatMap(JsValue thisObj, JsValue[] arguments), like we have for the already implemented Array.flatMap.