I think it's a mistake to see Dart primarily as an alternative to Javascript in the browser. While this is certainly how Google initially tried to market it, Dart always was designed around having its own VM, and as a result, it is actually more of a competitor for Python, Ruby, or Node. Even the original move to provide an alternative to Javascript in the browser was not primarily because Dart was a different language, but because the Dart VM wouldn't be constrained in the same way that Javascript VMs were.