The chart legend is confusing...

• "dart" means "handwritten Dart running in the Dart VM"

• "v8" means "handwritten JavaScript running in V8"

• "dart2js" means "dart2js-generated JavaScript running in V8"

I can't find any link to the actual handwritten JavaScript (or the handwritten Dart) that these benchmarks are based on. Without this, it's impossible to know the value of these numbers.

Maybe the handwritten JavaScript is written really badly. Maybe the procedure performed by the respective languages is something that dart2js is particularly good at optimising. Who knows.