Lars Bak: To contrast these two languages, TypeScript is a safe bet... where Dart is trying to change some of the fundamental issues with JavaScript. I feel, from a computer science background, I still have problems that you can design applications with libraries where you can monkey patch the libraries when you get up running. I find that very, very disturbing when you are trying to write big applications. [with TypeScript] you end up in the same mess.
Anders Hejlsberg: Everything you say and more I will agree with. The question is not whether JavaScript is broken. The question is whether it is broken enough to merit being replaced by something else.