Comparison of Javascript with Google Dart

You can read about Dart at http://www.dartlang.org/docs/getting-started/ Some of the things I found good about Dart are :

1. Limitation is that any performance-wise advantages will be limited to Chrome only.(as,currently only V8 supports) .And for using on other browsers you might need to run some script to convert.
2. good point is that it has native support.
3. A very critical issue with JS is handling concurrency. Dart has "isolates": these are used for handling concurrency: It might look like a game changer yet to see if it fully working yet.

I would say its too early to say which is better.

If you read the nodejs google groups thread about dart you will see the community reaction is

We have better things to do then waste time looking at dart. Maybe google should put those resources back onto V8 rather then writing yet another mediocre language that doesn't solve any problems

Now, once the dart VM is supported by all major browsers, then we will look at dart seriously.