Knockout.js 2.2 主要改进内容包括：
- The with, if, and ifnot bindings have been enhanced to preserve their original DOM elements on initial binding, so they are lighter and won’t unnecessarily strip out any special behaviours inserted by third-party libraries. I know a lot of people asked for this.
- The dependency detection mechanism is now smarter in many places to avoid registering subscriptions that would be unnecessary no-ops
- Support for IE10 (well, we basically already supported it, but there was one edge-case issue with autocompletion that we fixed)
- Improved AMD support (the ko variable is now available in the context of all custom binding handlers, even if it isn’t in global scope)
- The text binding can now be used in a virtual element (e.g., <!--ko text: myValue--><!--/ko-->)
- Observable and computed properties have a new peek function for advanced control over dependency detection