DynamicHostObject in V8: function is invoked as property

[DavidBal]

Hi ClearScript-Team,

i have a problem when using the DynamicHostObject with ClearScript.V8:

const comobject = COMObjectProvider.createCOMObject("Excel.Sheet");

comobject.Application.Workbooks.Open("C:\\temp\\Sample.xlsx");

The Open function call, invokes the TryGetMember function on the DynamicHostObject.

Is there any way that function calls invokes TryInvokeMember function on the DynamicHostObject directly?

(I think the problem is that every function on a object in js is a property which returns a delegate/function "object".)

Kind regards,
David

[ClearScriptLib]

Hi David,

I think the problem is that every function on a object in js is a property which returns a delegate/function "object".

That's correct. V8’s embedding API mirrors JavaScript semantics, in which there's no method call primitive. Instead, method call syntax is desugared into property access followed by a function call. Embedders like ClearScript can intercept those individual steps, but V8 provides no hook for intercepting the combined operation.

When asked to retrieve a property that's actually a method, ClearScript returns an invocable object – a host method. V8 recognizes that as a function and calls it. That's how all .NET and COM method invocation works in ClearScript with V8.

Thanks!

[DavidBal]

Hi,

thanks for your input.

I got it working by returning a "methode"-class derived from DynamicHostObject which implements TryInvoke and knows the object and the methode name to invoke.

Is there a other way that you would preference?

Kind regargs,
David

[ClearScriptLib]

Hi David,

Is there a other way that you would preference?

If you don't need the method object itself to be dynamic, you could return a delegate instead. That could give you a performance boost as well. For example:

public class MyObject : DynamicHostObject {
    private readonly string instanceName;
    private readonly Dictionary<string, object> memberMap;
    public MyObject(string name) {
        instanceName = name;
        memberMap = new Dictionary<string, object> {
            { "foo", new Func<int, string>(Foo) }
        };
    }
    public override IEnumerable<string> GetDynamicMemberNames() => memberMap.Keys;
    public override bool TryGetMember(GetMemberBinder binder, out object result) => memberMap.TryGetValue(binder.Name, out result);
    private string Foo(int arg) => $"Foo({arg}) called for object '{instanceName}'!";
}

Good luck!

[ClearScriptLib]

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