One theme for Web platform improvements over the last few years has been stripping away the limitations that have characterized Web applications compared to desktop applications. So we support drag-and-drop, we compile JS to machine code, we offer fancy graphics, we let Web apps run offline, we give them writable local storage. A natural question is: what, if any, are the essential differences between Web apps and "desktop" apps? Will they converge completely?
I don't think so. Here are features of Web apps that I think are essential:
- URL addressing You access a Web app by loading a URL. You can link to Web apps from other Web pages, you can save URLs in bookmarks or desktop shortcuts, and you can pass around URLs to your friends.
- Always sandboxed Users are not able to make good trust decisions, so apps must always be sandboxed. One of the themes of Web platform evolution is finding ways to design APIs and browser UI so that we can safely grant access to platform features to untrusted apps. For example, Web apps can't be granted general filesystem access, but we can satisfy most needs with per-domain persistent storage and and the trusty <input type="file"> control to grant an app access to particular files.
- Browser chrome Web apps are used in the context of a browser. Forward and back buttons are available (and usually work!), providing a universal navigation UI across applications. Bookmarks are available, status is available, history is available, reload, stop, tab organization, etc. A lot of designers wish they could escape from the browser chrome, but sandbox requirements make that unrealistic, and the comfort of common browser UI should not be disregarded.
- Open box Web apps have internal structure that is exposed to the browser and to tools based on the browser. This enables tools like Greasemonkey to reach into and manipulate Web content. It enables browser features like text zoom and "find in page". It enables search engines. It allows for user style sheets and other kinds of end-user customization of the Web experience. It also creates an environment of pseudo-open-source-software, where authors can learn how other apps work, even if they can't modify or reuse that code directly.