The big question among Web developers has been whether browser and platform makers are simply leveraging HTML5 as an open-ended means to a closed end: specifically, as a standard language for producing native apps for multiple platforms, as opposed to a single, cross-platform app that plays for all. That question may very soon be rendered moot if and when the leading producers of JavaScript libraries render native-looking content using cross-platform code.

That day may be drawing very close. Last week, Michael Mullany, the CEO of Sencha - whose Ext JS library renders spectacular content on multiple browsers regardless of platform - gave an early nod of approval to Internet Explorer 10, the HTML5 rendering engine for Microsoft's forthcoming Windows 8.

"Simply put, (and with the caveat that we were running on the notably overpowered developer preview hardware) the IE10 HTML5 experience is one of the best we've seen on any platform to date. After a decade of Web neglect, Microsoft is back with a vengeance," Mullany wrote for his company blog. Listing the various HTML5 components IE10 will support, he added, "Remarkably, particularly for developers trained to look out for Microsoft platform tie-ins, there are none on this list. Microsoft simply implemented the draft standards with no extensions or gotchas."

At the forthcoming SenchaCon conference in Austin, Texas in late October, Sencha is expected to unveil (or have already unveiled) the first public beta of its Sencha Touch 2 JavaScript library. Its purpose will be to present a normalized set of tablet-oriented functions, enabling the same apps to play on iOS and Android platforms. It's a touch-sensitive version of Ext JS, which normalizes the processes of event handling and layouts, and fills in some of the gaps between what HTML5 is expected to support and what these platforms actually do support.

That public beta was expected to go live sometime this week, but was postponed. We've known for some time Sencha is working toward Windows Phone 7 support. Could the development team be planning an early experimental round of support for the Windows 8 Developers' Preview as well, and could that be behind the delay?

RWW put that question to Sencha's senior director for product management, Aditya Bansod, who gave us this response: "We're excited about Microsoft's focus on HTML5 and touch-based interfaces. We'll be adding support for Windows 8 in the future as a part of our roadmap. In the nearer term, we'll be adding support for Windows Phone 7 in the Sencha Touch 2.x family of products, and then Windows 8 at an appropriate time in the future."

Bansod's careful distinction between version 2.x and Windows 8 support points to the likelihood of Windows 8 being supported in version 3. Since Touch 2 also promises native app packaging - the ability for a cross-platform app to be distributed on native app stores like iTunes App Store and Android Market - outright Windows 8 support will have to wait for Microsoft to construct both the operations and the polices around its Windows 8 distribution outlet, currently called just "Store."

In any event, the probability is now great that a plug-in-free JavaScript library will enable a class of mobile apps that can run on multiple mobile platforms as native apps.