The ArcGIS JavaScript API Web Optimizer is a web application that will generate custom or lightweight builds of the ArcGIS JavaScript API. You can pick and choose the component you want, then generate your custom/slim version of the API. You may have heard about this at the Esri Dev Summit this past year, but things went silent for a while after that. However, a recent blog post by Esri has surfaced with a link to the open beta site.

Once a custom build is created, you can download a copy or have it hosted on js.arcgis.com (with an Organization or Developer account). The Esri CDN is still available for both the regular and compact builds of the API and this new offering expands the options available to support growing variability of Dev requirements (based on developer requests I’d imagine).

Why might you want to use this approach? Esri’s documentation explains some benefits:

The Web Optimizer offers an alternative to the “one-size fits all” builds that Esri offers via the CDN (js.arcgis.com/3.9/ and js.arcgis.com/3.9compact/) or as a download. This works well for development of smaller web applications. But as applications grow in size and functionality, this approach breaks down. When an application uses a large number of modules not included in the available builds, applications generate more http requests, download more JavaScript and take longer to load. A custom build combines the required modules which reduces the number of http requests and application load time.

I wish this was around in the ArcGIS JavaScript API version 2 days! Back when smart phones and tablets had limited memory and bandwidth. Moving forward I would think new devices are able to handle the standard/compact CDNs while leveraging the benefits of pre-caching, distributed servers, and bypassing old browser single-domain download concurrency limits (default is 5).

On the other hand, long wait times (and progress bars) for [down]loading applications is a UX no-no. The Adobe Flash loading bar, and Silverlight’s Blue Circle-of-Wait rank up there with the Windows XP 99% complete progress bar - why does the last 1% take forever?! I can’t get a coffee every time I see these - I drink enough java as it is! The ArcGIS JavaScript API Web Optimizer is one way to combat such issues. Wouldn’t you choose the shorter line at the grocery store?! Log in and try the beta for yourself.