They touch on the importance of compiling to efficient JavaScript in their FAQ https://www.dartlang.org/faq#q-why-isnt-dart-more-like-haskell--smalltalk--python

They touch on the importance of compiling to efficient JavaScript in their FAQ https://www.dartlang.org/faq#q-why-isnt-dart-more-like-haskell--smalltalk--python--scala--other-language https://www.dartlang.org/faq#q-why-isnt-dart-more-like-haske... But it probably also helps that one of dart's creators, Lars Bak also developed the V8 JavaScript engine.