JavaScript is relatively fast, but it can always go faster. Read more about how to optimize your JavaScript for performance.
How to write low garbage real-time JavaScript from Scirra, the HTML5 game making tool.
Optimizing for V8 - Introduction is written by Florian Loitsch, engineer on Dart's JavaScript generation.
Optimizing for V8 - Inling, Deoptimizations is part 2 in Florian's series.
From Console to Chrome - HTML5 and JavaScript for game developers from Lilli Thompson, Chrome Games engineer.