Haxe's document says that catching exception thrown by safe cast is better than checking the type with Std.is, but that's not true on V8 JavaScript engine.
V8 JavaScript engine cannot optimize functions containing try-catch block. If you are sure that the function you wrote will be called frequently, you should not use try-catch in that function.
This seems to be V8-specific, but should this be stated in official document?
https://code.google.com/p/v8/issues/detail?id=1065
http://haxe.org/manual/expression-cast-safe.html