At work I am required to write a web UI that has a rich-desktop kind of interface. Without getting into too much details, it's layout will look a bit like an older email application(e.g. outlook, the older versions). It also need to have drag-n-drop capabilities. I whipped up a prototype of the UI using prototype and scriptaculous, since that's what I've been getting fluent with. A couple of things about my prototype made me decide to give Flex a try.
- No draggable divider. The draggable divider - although not essential - is something that seasoned computer users have learned to expect when you give them interfaces that have multiple panels jammed onto one screen. Scriptaculous didn't have an draggable divider widget. YUI and ExtJS did, and I am not against learing a new library. But I get the vibe that their implementations might not be rock solid.
- Buggy drag-n-drop libary. Scriptaculous comes with a drag-n-drop library. I've used it in multiple occations. It's also been buggy for me on multiple occations. A lot of the bugs are attributed to differences in browsers.
I decided that I was tired of chasing down cross browser bugs, which will only grow exponentially the more complex my UI gets. Therefore, Flex could really be the answer to these problems.
I am probably 60% done with my port of the UI prototype from Javascript/prototype/scriptaculous to Flex. I am happy with it for the most part. Here are my first impressions of Flex. First the pros:
- Programming in Flex is suprisingly similar to programming in HTML/javascript/CSS. (Well, not as suprising as it could have been since I've heard Charles Lowe say the same on DrunkAndRetired.com podcast). You write a mxml file, which is like your markup - in place of your HTML; you write ActionScript inplace of Javascript; and there's a css 3 compliant stylesheet you can use to style the UI.
- Flex has a rich UI component model that similar to many of the desktop UI toolkits(Swing, GTK, MFC, etc), which is a departure from the HTML/Javascript model. This is a plus because you get a lot of widgets you can use out of the box with very little code. Using third party Javascript widgets is usually more involved.
- ActionScript is not much different from Javascript, so people literate in Javascript should pick it up easily. The only significant difference I've noticed so far is the type declaration syntax - ActionScript is statically typed. I believe ActionScript is compatible with a newer version of Ecmascript which has optional type declaration for variables and parameters. Type declaration in ActionScript(as far I can tell) is required on function parameters and global variables(errors out if you leave it), and optional on local variables(warns you if you leave it).
- Yes, you have to write XML, but it's not that bad. I have expressed my hatred for making programmers read and write XML by hand in the past. It's inhumane! Flex makes you do that. Yes. But! It's used in a way that's not as bad as some other ways in which XML have been used(build scripts, web configuration, for example). In Flex, XML is used for Markup (wow! a markup language used for markup? what a concept?). The XML declaratively defines the UI(such as in HTML), which, I my opinion, is the way UI's ought to be written, and not in a procedure way(such as in Swing).
- Flex components look good by default. For HTML/CSS you always have to design your own theme - even if you just want it to look half way decent. No such BS in Flex. Flex components look good out of the box(no CSS tweaks or includes required), because of this I believe you can prototype Flex UIs faster.
- A Flex app runs exactly the same on any browser it supports. This was the main sell for me. Nothing more needs to be said.
Now the cons:
- Development feedback - not as instant. Developer feedback loop is slower because of the compile step. ActionScript is a compiled language, and you need to compile your Flex programing to get a SWF file. Also, in Flex 3, they took away the eval() function(why oh why???). This means you cannot create an interactive shell in Flex like Firebug or the python shell.
- Mandatory Static typing. Although I have nothing against static typing in general. I don't like mandatory static typing(such as exists in Java, C#, C++). Haskell is a staticly typed language, it verifies all your types for you, and yet it doesn't require you to specify the types of all you variables and parameters because it can infer them all for you. I like that. This is not a big issue for me, it's just not as kosher as Javascript in this respect.
It's annoying that you have to write mx: to begin all Flex component tags in the mxml spec. No such BS in HTML. I tried a hack to do without it, it didn't work so well.
Update: Looks like I have gotten rid of the mx: problem. I guess I showed them ;)
Overall, the pros are worth more than the cons. Linguistically, I prefer Javascript to ActionScript and HTML to MXML, so it's not going to Change My Life(TM). But the UI component model and cross browser compatibility greatly outweigh those nags.