Meanwhile a few game engines have evolved based on HTML5+JS providing gaming features like collision detection, physics engine, WebGL support. Here is the list of a few that you can try to develop your own games for web and for mobile too.
❶ limejs: provides HTML5 framework for touchscreen and desktop browsers.
❷ ImpactJS: Not a freeware. Probably most popular among the list. Supports most of the browsers both on mobile and desktop.
❹ SnechaJS: It provides more than a game engine. UI framework, Charting solutions. Giving serious threat to Adobe Flex.
Crafty: Small sized provided nice set of gaming features.
❻ Construct2 from Scirra: Another commercial one