Dart 2.0 adds "strong mode," which ensures programs that violate Dart's type system will not compile, similar to JavaScript's use strict directive. page 
What is Strong Mode?
“Strong mode is a sound static type system which uses a combination of static and runtime checks to ensure your code is type safe—that you can never see a value whose runtime type does not match its static type,” according to the FAQ page. “With strong mode enabled (in an implementation that has both the static and runtime checks), Dart is a type safe language ensuring that static type annotations are actually correct at runtime.” page
Dr.SES
Which brings up JS Strong Mode ('Miller Mode') Discussion: The Frozen Realms proposal. page
Because an immutable root realm is transitively immutable, we can safely share it between ECMAScript programs that are otherwise fully isolated. This sharing gives them access to shared objects and shared identities, but no ability to communicate with each other or to affect any state outside themselves. We can even share immutable root realms between origins and between threads, since deep immutability at the specification level should make thread safety at the implementation level straightforward. page
See Also: Flutter: A beautiful mix of React and Dart for mobile SDK page