We recently developed a YAP app (I like the way that sounds) for a client. For those who are not familiar with YAP, Yahoo! describes the Yahoo! Application Platform:

The Yahoo! Application Platform allows you to reach our users and improve the Yahoo! user experience by building and deploying new experiences for them into Yahoo! pages, writing code the way you love to write it.

From a marketing perspective, it’s Yahoo!’s response to Facebook’s popular application platform and MySpace’s OpenSocial, but in many ways it is different (and it promises to be even more different in the future).

Here are some of the similarities and differences between YAP and other popular application platforms:

• Like Facebook, the YAP official SDK is PHP-based, and similarly both platform support development in Adobe Flash. Both also have their own markup languages (FBML,YML) and both support Javascript (FBJS,Caja).
• Unlike Facebook and OpenSocial’s “externally and internally facing” applications (seen by others and yourself), Yahoo! applications are “internally facing” (seen only by you) and thus are designed to work with My Yahoo! (and Yahoo Mail)
• Unlike Facebook and OpenSocial, very little interactivity is currently is supported on the front page/Small View
• The application metaphor behind YAP is probably more similar to those of “starting page” widgets for services like NetVibes and Pageflakes
• Sharing of applications is probably less intuitive than Facebook but comes “automatically” with each application (since it is built into the application chrome rather than the application itself for the most part)
• The YAP API supports OpenSocial 0.8, but in general its PHP API is less complicated (and less featured) than Facebook’s. Full support for OpenSocial is planned in the future

Developer Do's and Don’ts:

• YAP’s Caja Javascript Sandbox is a bit unforgiving when it comes to spelling errors, and at the time we developed our application, there wasn’t a great way to debug these problems
• Be prepared to write your own XML parser (we did) since currently YAP’s flavor of Javascript limits some types of DOM manipulation. If you plan on using AJAX and XML, this may be an issue. I believe their JSON support is a lot better.
• Understand the limitations of different Views. The Small (front-page) View doesn’t support Javascript, Flash or IFRAMES, so interactivity is limited. If you want to update the Small View, you’ll need to periodically run a CRON job or use a Web Service. Plan on doing most of your “work” in the Canvas View, which does support Flash and Javascript (but not IFRAMES).
• AJAX and other communication and event-based calls will need to be done through OpenSocial 0.8, so previous MySpace development experience helps
• The Yahoo! developer forum does a fairly good job of answering questions so be sure to use it. The individuals responsible for evangelizing and supporting the platform did a phenomenal job in supporting our development efforts. The documentation was okay (navigation wasn’t great), sample code (at least when we used it) was okay as well but could have been organized a little better.

Conclusions:

• Developing on YAP!, as is the case with any new developer platform, was challenging but fun!
• YAP! holds a lot of promise as soon as Yahoo! was more aggressively promoting.
• Remember that for the most part, the platform is still in beta, so some of these issues have probably addressed.