If you look at https://www.dartlang.org/performance/ https://www.dartlang.org/performance/ it looks like performance of js vs. dart2js is basically a wash. One

If you look at https://www.dartlang.org/performance/ https://www.dartlang.org/performance/ it looks like performance of js vs. dart2js is basically a wash. One benchmark is much faster in js, one much is much faster in dart2js, two are slightly faster in js, one is slightly faster in dart2js. The DeltaBlue benchmark highlighted in the article you linked to is now faster in js than dart2js. But one wonders what those plots would look like with another js engine, since dart2js is presumably optimized to emit code that v8 can optimize.