Minor optimization requested in https://bugs.webkit.org/attachment.cgi?id=387361&action=review#line1046 It might be worthwhile to pre-calculate the result of 'shouldCreateLexicalSCopeForClass' and 'hasInstanceFields' during parsing, or otherwise cache the value after the first calculation. Reasons for not doing this: it makes things like AST rewriting a bit more awkward and error prone (but, AST rewriting is not as common in JSC as in v8), and the hit from walking property list to determine these features might not be significant as they are not believed to be invoked frequently. It warrants some investigation.