I'm thinking of writing a realtime web app that would need to be able to push messages to the browser. When I first read about Comet, people seemed to consider it a brittle and immature approach due to weak browser support. Today, it seems to be an established and practical technique. But as far as I know, browers don't support the basic methods (long polling, iframes and script tags) any better now than they did in '06 when the idea first became popular.
Of course, it's difficult to manage all of those connections on the server side, but Comet frameworks solve that problem (and it was doable even back in '06 with something like Twisted). So what's the deal: are there any deal-breaking problems with Comet support in browsers, or were the people back then just wrong?
Also: I recently read a ~2010 blog post summarizing the state of Comet technology, covering each method in detail. It made it sound like none of the methods were really viable. The post was very persuasive, which is why I'm still edgy about Comet. The only thing I can remember about the blog is that it had a dark background (brown or black). Has anyone else seen that post? I'd really like to read it again.
I would argue that comet is very viable right now, every browser supports long polling so you have a common fallback that will still work, and there are methods in each browser that will be more performant than long polling.
You just don't see it very often because its quite a big undertaking to support the different methods in each browser, google and facebook have the resources to do it, but your average joe web dev. would be wasting a lot of time for very little gain. There are only so many applications where you really need the real time communication comet provides.
I think now with frameworks like APE and cometD that give you the backend and the client side utilities you are seeing more people able to take on the complicated tasks. It can't be immature anyway, comet is just a technique that uses existing capabilities in a very novel way.
I don't think that the browsers have changed much with respect to comet everything remains as it was a few years ago. With all of its hackiness intact. WebSockets will be the eventual answer so browser makers are in no hurry to fix commet, but that "standard" is still in flux.
Related
I am starting server side programming with RoR. I am noticing that it's tightly coupled with css/html web design. (Maybe I am just perceiving it that way since this is my first time doing server side stuff).
I just want to know, are server side programmers usually well knowledgeable in css/html layout stuff? I understand the ruby part, but css is giving me a headache. Debugging with different browsers/testing/ a lot of trial and error and still buggy. Finally you get it to work with Firefox and I.E doesn't work anymore...
How do server-side programmers out there usually tackle the "looks"/UI? Do they get someone else to do the css stuff and worry mostly about the functionality?
Thanks.
I answered a similar question here.
Most of the times from something basic, like twitter-bootstrap is now fantastic to get something up and running quickly.
What happens next is up to you: either you have some interest and learn some design skills. Or you get in touch with a designer to do the designing for you. I seriously think you will need to have some HTML/CSS skills yourself, but that is not the same as designing.
It depends on the development shop your working for I suppose. Larger companies tend to have some people focus on the backend, and some on the front end to best suit peoples talents.
I would highly recommend becoming familiar with the front end UI as well for your own benefit though. Most small web development shops are seeking full stack developers that can manage all aspects of the web app from server configuration, backend logic, and UI. You'll be much more well rounded in solving your own challenges, and become a more valuable employee with a diverse skill set.
Since your using RoR I would recommend becoming familiar with SASS and Coffescript since they can save a lot of development time. Also sass provides excellent mixin features to help solve your CSS cross browser issues, which you can find several prepackaged ones in Thoughtbots bourbon gem. https://github.com/thoughtbot/bourbon
The question is impossible to answer.
Many server-side devs are well-versed in HTML, CSS, and JavaScript, at least up to the "Oh that's the IE7 off-by-one bounding rectangle absolute-div positioning bug" point.
However, I think some groups of server-side devs are generally more adept than others: server-side environments like RoR, PHP, and so on tend to push more HTML/CSS onto the devs than, say, Java.
For me, the trick has been to keep the HTML and CSS relatively clean (sass/scss helps a lot), not obsess about pixel-perfect cross-browser appearances, and have layouts that you don't have to mess with much. There are HTML/CSS frameworks that help in this regard.
Conversely, a lot of designers don't know enough JavaScript to be useful--I think it is important for site developers to know enough JavaScript to provide the necessary functionality. Here again, the frameworks tend to breed different levels of JavaScript awareness, although that's changed somewhat as more sites get more interactive.
This question is a bit of a shot in the dark and Im not even sure it makes sense at all.
Still : Im quite used to the good ol' LAMP server design but tend to feel I could use some good push technology instead of the very inefficient repeated AJAX calls to pull new data, if any. Is there any way to achieve this without Java servlets (ie using Apache/PHP) ? Is HTML5 giving any hope for a step in that direction ?
I looked into Comet technology but it looks like it's just long-polling AJAX, which is just faking a push technology (I don't really know but it doesnt sound like an efficient way to do push... just a way that works).
I'd suggest reading this: http://today.java.net/article/2010/04/26/html5-server-push-technologies-part-2 as an introduction to HTML5 web sockets and http://www.indicthreads.com/1525/building-real-time-web-applications-using-html-5-web-sockets/. Further Google searches will yield a lot more info. This looks like the way to do push in the most capable browsers as it has advantages over the altenative pre-HTML5 technologies.
As for PHP being the server end point, here's some reading: http://code.google.com/p/phpwebsocket/ and http://www.murraypicton.com/2010/07/websockets-and-php/ and it sure look possible.
The disadvantage of using HTML5 websockets is that it's only supported in some browsers so if you want wide cross-browser support, you will also have to implement an alternate method.
I am learning how to program and my goal is to build a simple functional prototype...I'm at the very beginning.
I am not concerned with the visual design at this stage, other than as it relates to being able to demonstrate the functionality.
My question is: do I need to worry about ironing out cross-browser bugs in the HTML/CSS, or can I do development on a single browser? (Perhaps a better way of asking this is does the back-end programming have any effect on which browser is displaying it).
If you are at the very beginning and only want a functional prototype, do not worry about cross browser HTML/CSS. In fact forget the CSS altogether and focus on printing just standard HTML. Since the visual design will change, focus on the content, styles can always be applied and switched later.
If you need Javascript/AJAX stuff I would recommend using a library like JQuery that has already solved many cross browser problems for you.
The back-end stuff "Perl, PHP, Python, etc" shouldn't care about the browser as it is simply printing text for the browser to render as it will.
The back-end programming will affect the way a given browser displays your page and there might well be two schools of thought on whether you should be picky about the browser compatibility issues.
On the one hand, if you're just finding your feet in web development it might be asking too much to expect to have a standards-perfect, cross-browser site or application every time. It might be better to focus on actually accomplishing a finished result and learning as much syntax and technique as possible.
On the other hand, it might be argued that it's a good idea to get into the habit of adopting good practices now and recognising the sorts of things that are going to give you headaches... probably when you view your page in Internet Explorer. This takes more time to reach a finished product, but it would teach you good habits up-front.
Really it comes down to your own approach and preferences. Do you want to be detail-oriented and turn out a polished result in a longer period of time, or would you prefer to just get to the finish line and identify issues on a case-by-case basis?
Do car prototypes have a working stereo, leather upholstery, chrome rims, dice, and other random stuff which does not demonstrate the functionality of the newly-designed car?
My rule of thumb is that if it takes you more than 10 minutes to make it look acceptable to others (I'm completely fine with a disgusting design when prototyping), you're spending too much time on the aesthetics and less time on the actual clockwork.
What good does a "pretty-looking" site do if it has no functional layout?
This depends on both your audience and on your tooling. If you are trying to support all users on all browsers, then you will certainly need to do testing on those browsers (although actively developing on those browsers may not be necessary), whereas if you only need to support WebKit-based browsers (Chrome, Safari) or WebKit-based browsers and Firefox, that is less testing that you need to do.
It also depends on your tooling. For example, if you are writing directly in HTML and CSS, then you are much more likely to run into browser compatibility issues. However, if you use a tool such as GWT, which can generate browser-specific output automatically, there are fewer such issues to deal with.
Note that you can use Selenium (aka WebDriver), to automatically test your code on multiple different browsers, even if you only actively develop within a single browser environment. That way, you can know if you've broken something, but not have to constantly manually test in multiple browsers.
I want to make a site from scratch, and Im considering to use Flex to make a R.I.A instead of the standard approach (xhtml + css + some ajax).
The kind of site I want to make is something like e-bay, but less complicated.
But.. I know that 95%+ of the sites like that are built in the previous mentioned techs... so, what are the cons and pros if I want to make a pure Flex site?
Thx.
If you write an entire website in Flash, the entire website lives at one URL. (Short of mucking around with whatever Flash provides to let you offer deeper links.)
Whereas a website written in HTML, unless you go mad with your AJAX, lets people link to the stuff they’re actually interested in, like unicorns:
http://cgi.ebay.co.uk/DESPICABLE-ME-AGNES-Unicorn-Doll-Plush-Character-Doll-/180602861597?pt=LH_DefaultDomain_0&hash=item2a0cc4f81d#ht_1755wt_907
Or for a non-eBay example, Stack Overflow questions:
Flash for business web applications - why not?
HTML also has a pretty standard and understood user interface: links, and form controls. (Mainly links.)
Flash doesn't work on iPhone/iPad. End of story.
Other reasons: not a web standard, often quite slow, not good for SEO, etc.
It requires users to have a proprietary plugin which some users don't want and other users can't have (since isn't available for all platforms (iOS being a key example)).
It also has performance and stability issues on some platforms (OS X and Linux being prime candidates).
While some search engines have started to index Flash content (so long as it exposes the information), the results aren't as good as for content rich HTML sites.
You can do that simply using traditional xhtml + css + jQuery (or any JS framework if you want to increase UX). Flex won't do much in your scenario.
In my experience, performance is not a real issue unless you play video - one can write bad programs in JavaScript, too...
Your pros are mostly on the development side: You can have a great looking site quickly, and you can almost completely forget about browser incompatibilites.
You rely on the customers having the plugin installed, though, and you rely on Adobe's technology for development and playing of the content.
If this is not important to you, and you can afford to do without all iPhone and iPad users, accessibility and standards compliance... go for it!
Flex is good if you want to install as an application using Air. ebay actually has a RIA version, or at least they did for a while.
There are several concerns with a Flash site, some of which Adobe has addressed in the last couple of years.
One is accessibility. It is more difficult to make a Flash site accessible to the visually impaired, who use screenreaders.
Related, people like to be able to copy and paste content, as well as print. With standard web pages, the developer need do nothing to support this, it just works from the browser. With Flash, you'll have to take care to make your text content selectable, and I'm not sure a user could ever select a section of text + images. I've never done it, but I can only imagine that implementing printing ability in your Flash site would be nightmarish, at best.
Another is linking and addressability. For most sites, you can copy or at least get a link that you can share or save to get back to where you want to be. With Flash, you usually go to a single address and then the rest of of your experience happens inside the Flash "window" and the browser isn't actually navigating any pages. It is far more difficult to implement this ability in a Flash site.
A Flash site is usually very slow to load, especially the first time, and page load times are immeasurably important to a site's success.
Finally, you've perhaps heard the furor over the last couple of years about different vendors supporting or not supporting Flash in their products/devices. An all-flash site would be completely inaccessible on any iPhone or iPad, for example, which do not support Flash at all. Furthermore, some employers do not allow plugins like Flash to be installed on work machines, so you'd eliminate that portion of possible traffic, as well.
Nobody has yet mentioned Silverlight.?
I mostly agree with Jay's answer concerning accessibility, but as a further note would like to add that development in Flex/Flash vs HTML/CSS/JS could be more costly not only in terms of money but also for maintenance. Many Flex/Flash devs typically charge a higher price and their dev tools, which are necessary for compilation, usually aren't free, compared to HTML/CSS/JS devs, who often use freely available text editors.
Why HTML/JavaScript/CSS are not becoming compiled languages (or maybe even merge into a single compiled language)? What if browsers were running "Browser Virtual Machine" and html/javascript/css sources could by compiled to a "browser bytecode". Wouldn't it help developers and users a lot?
I can see a few challenges:
What to do with zillions of existing pages? Make this compilation optional, so if you want you can use plain old html. If you want to feed a browser with a compiled page just use .chtml for example.
How search providers would index pages? Make a decompiler that would decompile bytecode into exact original sources (for example like flash can be decompiled). Or search providers can use the same virtual machine and get data they need from there.
How to make it compatible with all browsers? Have one centralized developer (lets say w3c) to develop this virtual machine and then each browser would embed it.
But what about benefits:
Speed.
Size.
No more "loose" and "half-correct" html. It is either correct or won't compile.
Looks the same in every (supported) browser.
If not a bytecode then at least have some native compression going on, html probably is not the most efficient way of data storing. I know there is gzip but why to compress pages every time on a server and decompress in a browser if we can compress it once and feed it to a browser?
So what stops us from taking this road (well, besides a huge amount of effort to make it all happen)?
Ah, but Javascript IS becoming a compiled language. Check out Firefox 3.5 with TraceMonkey. It's insanely fast compared to um you-know-who's browser. It's true that JS will never be C, but it's a much more dynamic language than C is, and in many ways that makes it more expressive and powerful.
As far as HTML goes, I don't think that the lack of validity of HTML is a huge detriment to speed. I think the engines that put together the visual representation and manipulate the DOM need to get a lot better (um, IE, I'm looking in your general direction...). CSS compliance needs to get better, and CSS itself needs to get more powerful. (Get on the bus with CSS 3 people!)
But I do think that speed is going to get better on Firefox and Chrome to such an extent that people really ARE going to start using it for mainstream application development. It's funny. Adobe seems to be selling Flash as their platform for dynamic web content, MSFT is selling Silverlight for dynamic web content, and Google just wants to really improve HTML and Javascript to display dynamic web content. And Google's doing pretty well at it so far, I must say...
Your ideas have validity when they are applied to JavaScript. As others have noted, to one degree or another several vendors are trying to apply those principles to JS even now. Another big step in this area will likely be the Chrome OS Google has announced. However, when it comes to (X)HTML and CSS I think your ideas may be missing the point.
The world wide web is not a buggy and inconsistent application platform but a massive and unprecedented collection of interconnected documents. The power of the web is in the abstraction of the data from the often rigid (and breakable) visual layouts and increasingly complex in-page functionality largely provided via JavaScript. Encoding these pages in (X)HTML is ideal for making them accessible to the widest possible audience both in terms of browsers and in terms of technical knowledge required to author a page.
More and more the web is being used as an application platform - which is a powerful and exciting use of this technology - but we cannot lose sight of the fact that these Ajax-driven "web 2.0" apps are merely documents with extended functionality. Compilation doesn't make sense for a document and compression is already happening (via gzip and the like).
On a more practical note, the W3C moves at a glacier's pace and browser vendors take turns between jumping-the-gun supporting experimental features in unfinished specs and taking their sweet time supporting other specs which have been on the table and in common usage for years. The whole processes is like herding cats. I wouldn't hold my breath for them to make the kind of radical changes you're proposing any time soon.
Since HTML and CSS aren't code they can't be compiled. Google Chrome's V8 engine does actually convert JS into byte code, expect other rendering engines to follow suit!
http://code.google.com/apis/v8/design.html
We recently reworked a php template system I've helped create to use minify to compress multiple JS and CSS into one file each, seeing our file sizes drop to about 20% of the origial combined sizes. Minify also does gzip and caching so it's really amazing for speeding up websites.
http://code.google.com/p/minify/
In short you can't compile non-code, which HTML and CSS are. JS can be compiled and is starting to be, but all depends on what browsers feel like doing.
Browsers just need to be on the ball regarding supporting web standards. The more browsers do this, the less headache us web developers have. I was quite happy with YouTube's very public drop of support for IE6. We need more action like that for the web to move forward.
The V8 javascript engine (also embedded in Google Chrome, but it's open-source and liberally licensed so you're welcome to use it in the next browser you write!) does compile Javascript to native machine code -- of course, it does it "just in time" (like most modern compilers -- Java, C#, etc!), not "ahead of time" (like Fortran did in 1954 when computers were just too weak to handle compilation in the midst of execution). I'd be surprised if other good JS engines, like those in the very latest Firefox and Safari, didn't do the same.
Looks like you're not advocating "javascript as a compiled language" (since it obviously already IS compiled, if you're using a good JS engine), but rather "ahead-of-time" compilation for it (just when most modern languages are essentially abandoning ahead-of-time compilation). Pushing machine code rather than compilable code down the wire sounds like a mostly horrible idea -- much larger size, difficulties in supporting one CPU vs another, security nightmares in properly sandboxing it, etc, etc) with not much in term of compensating benefits.
That said, if you're really keen on pushing machine code to the client, try out nativeclient (as long as the client is an x86 machine - forget every smart phone on the planet, many netbooks, good old macs, etc) -- at least it promises a fix to the security nightmares. If and when you're happy with nativeclient, transforming a just-in-time compiler into an ahead-of-time one is a far easier technical challenge (if you want to keep using Javascript for the sources rather than other languages, of course).
See here for a previous discussion on the matter
Not all of the reasons given are necessarily valid, but one important one is that, unless you're Google, server-side CPU cycles are a lot more valuable than client-side cycles: so it's easier to have the client compile/optimize what is quite often dynamically generated HTML/JavaScript, rather than the server.
Ken
Speed.
You're assuming that it takes significant time to parse HTML. However it might be that that time is insignificant compared to the time required for something else, e.g. the time required to layout the text on the end-user's window.
No more "loose" and "half-correct" html. It is either correct or won't compile.
You already get that, using [X]HTML.
Looks the same in every (supported) browser.
You seem to be saying that there should only be one browser, or that all browsers would support it equally.
Internet standards don't happen by having a single body (the w3c) implementing something and declaring it a standard. Instead, internet standards happen by having multiple independent bodies creating multiple implementations. A consequence is:
Some people have developed something that isn't standard yet (i.e. they're ahead of the standard)
Some people haven't yet developed something that is standard (i.e. they're behind of the standard)
I think your idea is sound, however there's still no way to enforce a standard. Thus if there was a non-supported feature, there's a good chance the entire page would simply not display anything. In the current setup, critical information can still be passed.
Google V8, which is one of many new-generation javascript engines 'compiles' javascript into pseudocode, much like .NET 'compiles' c# on the fly. Nothing magical here. Expect more of it esp. as webapps get heavier and more demanding
HTML
HTML is pretty much XML. DTD'd exist for various versions and developers can check against that at any time.
CSS
CSS is not a programming language, however I do agree that "compiled" CSS could work seeing as compilation would compress it. However with the support that CSS has and with the number of essential hacks any CSS needs to have, you'd never manage to compile it without errors.
JS
As others have mentioned, JS IS becoming a compiled language except the browser compiles it for you and not you yourself.