[webkit-dev] why js script" var a = new XMLHttpRequest; ", it's ok; but "var a = new StyleSheet; ", it'll throw an exception?

[Suk Zhong]

Hi All:
   We're trying to extend WebKit dom js binding.We have some questions.

   in DOMWindow.idl having the following code:
   attribute StyleSheetConstructor StyleSheet;
   attribute [JSCCustomGetter] XMLHttpRequestConstructor XMLHttpRequest;

   and we find class JSXMLHttpRequestConstructor has function
getConstructData, while JSStyleSheetConstructor doesn't have function
getConstructData.

   if test the following js script:"var a = new XMLHttpRequest;", it's
ok;but "var a = new StyleSheet;", it'll throw an exception.

   and we trac this problem to Interpreter::privateExecute() and
JSValuePtr::getConstructData function

   inline ConstructType JSValuePtr::getConstructData(ConstructData&
constructData)
   {
        return JSImmediate::isImmediate(asValue()) ? ConstructTypeNone :
asCell()->getConstructData(constructData);
   }
   and we know this function returns ConstructTypeNone for
JSStyleSheetConstructor object,  ConstructTypeHost for
JSXMLHttpRequestConstructor object;

   JSStyleSheetConstructor object and JSXMLHttpRequestConstructor object are
returned by the same template function getDOMConstructor.

   our questions are:

   1.why it has this return?
   2.which codes make the two object have different immediate value?
   3.some people can explain the whole role of class JSImmediate?
   4.our trac maybe be not correct,who can explain why newing StyleSheet has
exception and newing XMLHttpRequest is OK?

Thanks and Best Regards

Suk
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