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Commented Issue: [BUG] JScript for..in loop fails in Standards Mode [94]

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It appears that the for/in loop is not working when JScript engine is initialized with WindowsScriptEngineFlags.EnableStandardsMode flag.

I tried adding PropertyBag and ExpandoObject as host objects.

I noticed that there is a ScriptEngineException when executing for/in loop on either of the two objects which has HResult of 0x800a0005 (Invalid procedure call or argument).

Without WindowsScriptEngineFlags.EnableStandardsMode flag everything works without exceptions.

I am developing on Windows 10 with ClearScript 5.4.3

Here is the sample program:

```
static void Main(string[] args)
{
var engine = new JScriptEngine(WindowsScriptEngineFlags.EnableStandardsMode);
engine.AddHostType("Console", typeof(Console));

dynamic expandoObj = new ExpandoObject();
expandoObj.testProp = "expando testProp Text";
engine.AddHostObject("expandoObj", expandoObj);

var propertyBag = new PropertyBag();
propertyBag["testProp"] = "property bag testProp Text";
engine.AddHostObject("propertyBagObj", propertyBag);

engine.Execute(@"Console.WriteLine('expandoObj.testProp=' + expandoObj.testProp);");
engine.Execute(@"Console.WriteLine('propertyBagObj.testProp=' + propertyBagObj.testProp);");
engine.Execute(@"Console.WriteLine('');");
engine.Execute(@"for (var item in propertyBagObj) Console.WriteLine('propertyBagObj[' + item + ']=' + propertyBagObj[item]);");
engine.Execute(@"Console.WriteLine('');");
engine.Execute(@"for (var item in expandoObj) Console.WriteLine('expandoObj[' + item + ']=' + expandoObj[item]);");

}

```

Comments: The problem is that JScript in Standards Mode slightly extends/breaks the `IDispatchEx` contract in order to pass extra data to the host. The extra data consumes otherwise unused argument bitfields and confuses the CLR's `IDispatchEx` implementation. We're testing a fix that installs vtable thunks that clear out the errant bitfields before passing the arguments through. This also fixes host property deletion.

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