The 5-10x difference mentioned is the difference in raw hardware speed between mobile CPUs and desktop CPUs, not a reference to JS speed vs native speed.
JS speed as compared to native depends heavily on the nature of the code being executed, how type-stable it is, how polymorphic it is, what its allocation behaviour is like, and a number of other factors.
JS speed as compared to native depends heavily on the nature of the code being executed, how type-stable it is, how polymorphic it is, what its allocation behaviour is like, and a number of other factors.