"Inversion of control" is a powerful design principle that we could use to improve the user experience of Drupal, and rival that of native applications.
I've made no secret of my interest in the open web, so it won't come as a surprise that I'd love to see more web applications and fewer native applications. Nonetheless, many argue that "the future of the internet isn't the web" and that it's only a matter of time before walled gardens like Facebook and Google — and the native applications which serve as their gatekeepers — overwhelm the web as we know it today: a public, inclusive, and decentralized common good.
I'm not convinced. Native applications seem to be winning because they offer a better user experience. So the question is: can open web applications, like those powered by Drupal, ever match up to the user experience exemplified by native applications? In this blog post, I want to describe inversion of control, a technique now common in web applications and that could benefit Drupal's own user experience.
Native applications versus web applications
Using a native application — for the first time — is usually a high-friction, low-performance experience because you need to download, install, and open the application (Android's streamed apps notwithstanding). Once installed, native applications offer unique access to smartphone capabilities such as hardware APIs (e.g. microphone, GPS, fingerprint sensors, camera), events such as push notifications, and gestures such as swipes and pinch-and-zoom. Unfortunately, most of these don't have corresponding APIs for web applications.
A web application, on the other hand, is a low-friction experience upon opening it for the first time. While native applications can require a large amount of time to download initially, web applications usually don't have to be installed and launched. Nevertheless, web applications do incur the constraint of low performance when there is significant code weight or dozens of assets that have to be downloaded from the server. As such, one of the unique challenges facing web applications today is how to emulate a native user experience without the drawbacks that come with a closed, opaque, and proprietary ecosystem.
Inversion of control
In the spirit of open source, the Drupal Association invited experts from the wider front-end community to speak at DrupalCon New Orleans, including from Ember and Angular. Ed Faulkner, a member of the Ember core team and contributor to the API-first initiative, delivered a fascinating presentation about how Drupal and Ember working in tandem can enrich the user experience.
Inversion of control in end user experiences
Ed's changes are not in production on Drupal.com, but in his demo, clicking a teaser image causes it to "explode" to become the hero image of the destination page. Pairing Ember with Drupal in this way allows a user to visually and mentally transition from a piece of teaser content to its corresponding page via an animated transition between pages — all without a page refresh. The animation is very impressive and the animated GIF above doesn't do it full justice. While this transition across pages is similar to behavior found in native mobile applications, it's not currently possible out of the box in Drupal without extensive client-side control.
These impressive interactions are possible using the Ember plugin Liquid Fire. Fewer than 20 lines of code were needed to build the animations in Ed's demo, much like how SDKs for native mobile applications provide easy-to-implement animations out of the box. Of course, Ember isn't the only tool capable of this kind of functionality. The RefreshLess module for Drupal by Wim Leers (Acquia) also uses client-side control to enable navigating across pages with minimal server requests. Unfortunately, RefreshLess can't tap into Liquid Fire or other Ember plugins.
Inversion of control in editorial experiences
We can apply this principle of inversion of control not only to the end user experience but also to editorial experiences. The last demos in Ed's presentation depict CardStack Editor, a fully decoupled Ember application that uses inversion of control to overlay an administrative interface to edit Drupal content, much like in-place editing.
Inversion of control as the rule or exception?
Those of you following the outside-in work might have noticed some striking similarities between outside-in and the work Ed has been doing: both use inversion of control. The primary purpose of our outside-in interfaces is to provide for an in-context editing experience in which state changes take effect live before your eyes; hence the need for inversion of control.
Thinking about the future, we have to answer the following question: does Drupal want inversion of control to be the rule or the exception? We don't have to answer that question today or tomorrow, but at some point we should.
In the longer term, client-side frameworks like Ember will allow us to build web applications which compete with and even exceed native applications with regard to perceived performance, built-in interactions, and a better developer experience. But these frameworks will also enrich interactions between web applications and device hardware, potentially allowing them to react to pinch-and-zoom, issue native push notifications, and even interact with lower-level devices.
In the meantime, I maintain my recommendation of (1) progressive decoupling as a means to begin exploring inversion of control and (2) a continued focus on the API-first initiative to enable application-like experiences to be developed on Drupal.
I'm hopeful Drupal can exemplify how the open web will ultimately succeed over native applications and walled gardens. Through the API-first initiative, Drupal will provide the underpinnings for web and native applications. But is it enough?
Inversion of control is an important principle that we can apply to Drupal to improve how we power our user interactions and build robust experiences for end users and editors that rival native applications. Doing so will enable us to enhance our user experience long into the future in ways that we may not even be able to think of now. I encourage the community to experiment with these ideas around inversion of control and consider how we can apply them to Drupal.
— Dries Buytaert