Dart (2011), TypeScript (2012) and CoffeeScript (2009) and arguably Haxe (2005) all competed in the same space. Google made a optics mistake embedding Dart into Chrome - people feared antitrust, but it is a significantly better language to use than JavaScript.. it's disappointing how that played out. Usability wise, Dart is similar to TypeScript, in many ways better (real type safety, null safety, not being hamstrung by down compiling to JS). Dart feels closer to C# in syntax, style and language features.. TypeScript is also trying to travel that way, but syntax is different, and it's still hamstrung by JS.
Dart as a platform provided the unique ability to target both JIT at development-time to enable sub-second hot reload and AOT for release apps, providing native performance when it comes to scrolling, animation, etc.