I am a knockoutjs lurker right now. Reading up on it and trying to understand how to use it because I have a project coming up. From what I see it seems great. There is even a Rails-knockout plugin to help bind the knockout objects to Rails models. I am excited about it. I think the binding of data to HTML elements is a perfect fit and natural extension of HTML. I briefly looked at backbone, but it seems very limited in the user experience portion of the puzzle.
backbone and knockout focus on two different problem spaces: app architecture (backbone) and UI wizardry (knockout).
there are several plugins for backbone that bring model binding and other user experience enhancements to it, though. plus, backbone integrates directly with jQuery, so you have access to all of jQuery's libraries and plugins, still.
There is so much proliferation of javascript mvc plugins. From a user point of view, makes deciding very difficult. I basically looked at the two big contenders and went with knockout because it solved what i thought was the more pressing issue. As for model persistence, for my use case, i don't mind if it is only updated to the server with a submit, then i will push some json to the server and i can parse the complex object to save it. It is the javascript stuff that wastes the majority of my time on complex 1 page apps and is why I wanted something to help clear that up. I am sick of writing jquery onchange and other event codes for select boxes, etc. It always seems like an after thought, but if we are designing our ajax functionality from the start then we need a library which can handle it. For instance there is no standard or canonical way to do multiple depdendent cascading dropdowns in rails. For that I will roll it out by requesting a complex object once, then binding the select boxes, and it's done. No onchange events and multiple ajax requests. Anyway there are so many javascript mvc frameworks and i am really not qualified to judge their programming merits. I just have to go with what is likely to be maintained in the future, what works, and what has good documentation and user groups.
