Probably the biggest difference between JS and whatever revision to it you like, and Dart, is that dart is early-bound. That means, you can't change the list of

Probably the biggest difference between JS and whatever revision to it you like, and Dart, is that dart is early-bound. That means, you can't change the list of methods or fields present on an object at runtime. It doesn't really make sense to ask "Why should I switch from a language I already love?" If you're already productive and love what you're using, then you should probably keep using it. There are people who want a language that is more modular, scales better than JS for programming in the large, for IDE tooling, or ahead of time compilation, etc. Take a look at the Dart spreadsheet Total for example (https://code.google.com/p/dart/source/browse/branches/bleeding_edge/dart/client/samples#samples%2Ftotal https://code.google.com/p/dart/source/browse/branches/bleedi...) I find this code a lot cleaner than JS versions I've seen.