No need to disqualify the answer. The point of my question was of course to learn about aspects of Javascript-the-language that make it intrinsically easier to

No need to disqualify the answer. The point of my question was of course to learn about aspects of Javascript-the-language that make it intrinsically easier to build a fast implementation for than building one for python. If there are just more difficult-to-implement features that is interesting as well (although it would be nice to know which ones).