Are Yahoo Cocktails the answer for cross-platform apps?

Yahoo (s YHOO) has a magic elixir for web developers frustrated by writing applications that must display on multiple devices. The issue of application fidelity across devices and browsers is huge and getting bigger with the exploding number of Android (s goog), iOS (s aapl) and other devices hitting the market. With so little standardization, there are myriad screen sizes and features just within the Android universe.

Yahoo’s two-part “Cocktail” offering comprises Mojito, a JavaScript application framework and Manhattan, a cloud-based Mojito hosted environment that layers higher-level services atop a basic Node.js server-side execution engine. Putting Node.js on the server and a “100 percent” JavaScript execution environment on the device lets the whole experience migrate back and forth, according to Daryl Low, Yahoo principal software engineer speaking on the Yahoo video announcing the products.

Developers often write much of their client code in JavaScript, but often have to resort to other languages — Java, (s orcl) Ruby,  Python — when it comes to writing server code that runs on the backend.  Being able to use a single language for both, is “Nirvana” for developers, according to Yahoo Senior Product Manager Renaud Waldura.

Yahoo used these technologies to build its new Livestand iPad magazine that went live on Wednesday.

Web developers are intrigued. “For iPhone and iPad(s AAPL), sometimes you can use the same code for both, but if you target Apple and Android, or even just all the Androids, it’s a real pain in the neck. You usually have to tweak a ton of your code and there’s really no way to test that code on all the Android versions out there,” said a Cambridge, Mass., developer who requested anonymity because of his company’s media policies.

He said what Yahoo proposes here  is slicker and more complete (in that it has the server side covered) than other tool sets he’s looking into, including PhoneGap and Toura Mulberry. That the Mojito-Manhattan tandem is backed by a bigger company than these small players may also make them more attractive to developers, he said. Yahoo has had its share of troubles, but it has also proven its engineering prowess with projects such as Hadoop, among others.

The fact that Node.js is in at the core of the server-side implementation is key. Developers building web-based, consumer-facing applications will need a lot of headroom to scale up if demand grows. Node.js gives them this ability.

Carl Brooks, senior analyst with Tier1 Research, is impressed. “It’s nice to see Node.js in there, underpinning a collection of web development tools. This is pretty much a grab bag designed to make neat-o web sites and mobile services, which is, to be fair, a pretty hot area,” he said.

“Anyway, it’s Yahoo! showing off some neat tricks. Not sure it’s going to save their business, but this is a stab at a state of the art webscale developer platform. Bonne chance,” he added.

As more consumers rely on mobile devices for more of their social and work computing, this need for easier development will only grow.

So, all you beleaguered web developers out there, what’ s your take on Yahoo’s cocktail?