It is interesting that they have a special, third-party mirror for China: [1]
Also, I don't like Dart after I used a site built with it by Google. As far as I remember, it was a Doubleclick for publishers or something ad-related. It was very slow, even in Chromium, all animations were laggy, and in Developer Tools I saw that it loaded megabytes of JS, compiled from Dart code. For example, a "What's new" widget was implemented as a separate app and loaded several megabytes of code including its own copy of a standard library. I would recommend against using Dart for Web sites.
Also, I don't like Dart after I used a site built with it by Google. As far as I remember, it was a Doubleclick for publishers or something ad-related. It was very slow, even in Chromium, all animations were laggy, and in Developer Tools I saw that it loaded megabytes of JS, compiled from Dart code. For example, a "What's new" widget was implemented as a separate app and loaded several megabytes of code including its own copy of a standard library. I would recommend against using Dart for Web sites.
[1] https://flutter.dev/community/china