I'm working on a project that requires previews for related websites. We've been playing with a couple ideas, and two that have come up are using a service to render the website and send back a screenshot, or fetching the website and loading it in iframes as a 'live preview'.
The team is convinced that the iframes are the better option, since they would be interactive, and allow for dynamic visuals to be previewed, but I have some performance concerns.
Just wondering if anyone could offer some insights here, without coding up a server to fetch the website content and forward it to the site. The designs would have about 5 images/iframes, relatively small ~300x500 pixels. Would loading the 5 iframes be analogous to opening those sites in 5 tabs?
To answer your question, yes, it is analogous to opening those sites in 5 tabs. iFrames build an entirely new page in memory, then add it to the page.
Besides this, iFrames have huge security issues, as you are accepting the providers code without question. You're always better off using ajax and injecting the code into your own DOM after some parsing, but I realize that sometimes options are limited.
Check out performance specs offered here.
I think the important piece of the above article is this:
Iframes Block Onload
It’s important that the window’s onload event fire as soon as
possible. This causes the browser’s busy indicators to stop, letting
the user know that the page is done loading. When the onload event is
delayed, it gives the user the perception that the page is slower.
The window’s onload event doesn’t fire until all its iframes, and all
the resources in these iframes, have fully loaded. In Safari and
Chrome, setting the iframe’s SRC dynamically via JavaScript avoids
this blocking behavior.
Related
I like them more and wonder why they are not more common. Explanations involving caching or SEO make sense to me, but I don't see them as directly driven by user experience considerations. In which way are traditional sites with page reloads better for the user?
Personally I think the best argument for normal page reloads from a user's perspective is that when you do that it's much harder to break many basic browser functions. In general the back/forward buttons work, bookmarking works, copying and pasting links works, history works, page titles work, getting an error page when a server call fails works, everything just works as expected. For free.
I have seen single page application implemented in a way that breaks one or more of the above more times than I can count.
It's naturally not a problem if you get it just right (and then it will in general be nicer to use), but not all sites do.
Just as an example here's a screenshot how a site that is a SPA and justifiedly so (they have a music player that you don't want to interrupt with page loads), broke a basic browser function in a way they might not even have thought of. I was trying to find a song I recently listened to but couldn't remember the exact title... but because of the SPAness the page titles weren't properly reflected in my browser history.
I'm learning about Chrome and Native Client.
Basically i want to increase number of pages that are prerendered
by chrome (now its just one page).
I was thinking about creating a extension that would
allow to prerender more pages.
Is this a way to go or am i left with hard coding it into Chrome and build from scratch?
EDIT
I started a bounty for this question. I would really appreciate some input.
No, there is no way to go, you would need to hardcode it in Chrome and rebuild as you noted.
As you probably already know, Chrome explicitly states that they currently limit the number of pages that can be prerendered:
Chrome will only prerender at max one URL per instance of Chrome (not one per tab). This limit may change in the future in some cases.
There is nothing in their supported API's or their experimental API's that will give you access to modify this. There is not a toggle in chrome://settings/ or chrome://flags/ or anywhere else in Chrome currently that allows you to change this. You can however use the Page Visibility API to determine if a page is being prerendered.
In addition to the one resource on the page that you specify using the <link rel="prerender" href="http://example.org/index.html"> you could also consider prefetching resources.
The issue with prefetching is it will only load the top level resource of at the specified URL. So, if you tried to prefetch the other pages, like so:
<link rel="prefetch" href="http://example.org/index.html">
...then only the index.html resource would be prefetched, not all of the CSS and JavaScript links containeed in the document. One approach could be to write out link tags for all of the contained resources in the page but that could get messy and difficult to maintain.
Another approach would be to wait for the current page to finish loading, and then use JavaScript to create an iframe, that is hidden off the page, targeted at the URLs you want to prefetch all the assets for. The browser would then load all of the content of the URL and it would be in the user's cache when they go to visit the page.
There is also a Chrome extension that combines these two approaches by searching for link tags that define a prefetch and then creates the hidden iframe causing the assets to be downloaded and cached.
If the goal is to optimize around client performance for navigating your site there might be other alternatives like creating a web application that uses a Single Page Application (SPA) style of development to reduce the number of times JS and CSS are loaded and executed. If you are a fan of Google then you might check out their framework for building SPAs called AngularJs.
If it was a good idea to pre-render more pages, Chrome would probably already do it. Pre-rendering too many pages will drain website bandwidth and possibly end up slowing down the whole web, which is the opposite of what you're trying to achieve. So it's most likely intentional that you can only pre-render a single page and you shouldn't try to break that.
Not possible. Chrome manages pre-rendering based on many factors. If this was possible, it could also be easily abused by many sites. You could, depending on your page, keep all content on one page.
HTML has had frames from early days, but they are deprecated in the latest version. Many browsers (I have tried with Internet Explorer) don't even display frames properly.
Why has this been done? What was the drawback in frames?
Jakob Nielsen wrote a 1996 column that criticized frames. Some key points:
Frames prevent users from properly bookmarking pages. When a bookmarked frameset page is loaded, users' previous mouse clicks inside the frames do not matter. Only the outer URL is saved, and users have to navigate to where they were manually.
Frames present challenges for printing web pages. Printing all the frames at once is not suited to the different dimensions of paper (and users can get only the first pageful that way). Users generally have to right-click the frame they want and choose the appropriate context menu option.
Users coming from search engines may not have access to navigational elements if they are located in another frame — they are directed to only that frame the search engine found the text in.
While "framesets" (the most common type used on late 1990s/early 2000s web pages) are dying, the iframe (short for inline frame) remains alive and well. In fact, recently iframes have been found useful in today's "mashup" web applications, and extensions to the iframe are currently proposed in the HTML5 specification.
For example, Facebook, in its API for app developers, uses them to seamlessly integrate third-party apps with their own site while minimizing the security risk. (In this model, all third-party code remains on a separate domain, which is good for security reasons.)
Frames are not deprecated in HTML. They are obsolete in HTML 5, and just discouraged before this version. This has been clearly mentioned in the specified links.
Not to answer the OP but rather balance the bashing of framesets.
I find them great and nothing comes close to them when you want your menu intact and still:
Visually incorporate 3-rd party pages/apps (phpmyadmin or similar)
Viewing doctypes other than html (pdf's or images).
Due to its width="x,*" you get a simple "responsive" behaviour.
Also, you can provide smooth menu-animations while fetching main contents.
Used with sense, they're super.
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I haven't used frames since 1998. They seem like a bad idea and in all my development I've never had a situation where frames were the right solution, or even a decent solution.
However, I'm now working with an internal web application written by another group and the entire site is built in a - header, left side menu, right side content - frameset.
For one, when VPN'd to my network I constantly get a "website.com/frames.html" cannot be found." error message. This doesn't happen when I'm on the internal network.
Second, the app has a built in email/messaging system. The number of unread messages is shown in the left side menu frame as "Messages (3)" but the count doesn't update as I read the messages. The developer told me since it was in a frame I needed to right click on the menu and 'Refresh'. Seriously????
So, my programming related question is, what reasons do you have for not using frames in a website?
Although they solved a problem at the time they were created (updating part of a "page" while keeping in place a non-updating part), framesets were criticised in terms of usability pretty much from the start, as they break generic functions of the browser, such as:
bookmarking, and copy-and-pasting URLs to share
printing the page as displayed on the screen
reloading the page: since the URL has generally not changed, you will often be taken back to the site's homepage or default frameset; manually reloading some frames is possible, but not obvious to the user
back and forward buttons are ambiguous: undo/redo the last frame change, or take you to the last time the URL bar changed?
The heaviest burden of avoiding framesets - including the same content on every page - is trivial to solve if you are using any server-side language to generate your HTML, even if all it provides is a "server side include". Unlike framesets, a server-side include could occur anywhere on the page; building a site with a server-side scripting language or templating system has other obvious advantages too.
There is still an advantage to being able to update small areas of the page without reloading the entire content, which can be achieved via AJAX. This sometimes leads people to create interfaces with all the problems of framesets outlined above, but that is hardly an argument in favour of framesets. Again, a site built with well-designed AJAX functionality can achieve things which framesets don't even begin to address.
One good reason to avoid frames today is they have been deprecated in HTML 5: Chapter 11 Obsolete features
11.2 Non-conforming features
Elements in the following list are entirely obsolete, and must not be
used by authors:
[...]
frame
frameset
noframes
Either use iframe and CSS instead, or use server-side includes to
generate complete pages with the various invariant parts merged in.
The #1 reason? Users hate them.
Even if they offered advantages in other areas (separation of code, application design, speed etc) they are part of the user interface. If users don't approve, don't use them.
Frames were vaguely useful when you had a static web site, to avoid repeating navigation menu in all pages, for example. It also reduced the overall size of a page.
Both these arguments are obsolete now: sites don't hesitate to serve fat pages, and most of them are dynamically built so including such navigational parts (or status, etc.) has no problem.
The "why" part is well answered above, partly by your own question (you hit a limitation, although it can be overridden with a bit of JS).
My number 1 reason not to use frames is because they break the bookmark (aka favorite) feature of browsers.
With the technology that exists today, frames have become obsolete. But if your legacy project still uses them, you can make the messages update with some ajax.
Just because of the cell phone iPad craze doesn't mean that highly functional full featured sites are suddenly "obsolete", and those who decided to make framesets obsolete seem to be the same complainers who never figured out their full potential in the first place, or maybe they're the lobbyists of the mega-corporate cell-phone and tablet makers who couldn't be bothered to make a decent frames capable browser for their itty-bitty screens.
Admittedly, iFrames can handle simple jobs like scrolling and/or displaying independent segments within a single page pretty well, and I use them for that inside my own frames based website, but to get them to work as well as the foundation for a site itself is a nightmare. Trust me, I know because my website is one of the most sophisticated frameset based sites on the Internet and I've been looking at the pros and cons of transposing it all to iFrames. Nightmare is an understatement.
I can already hear the whiners saying, "Well why did you build it that way in the first place then?" ... and the answer is A: Because I'm not lazy. and B: Because a frames based site is the most functional, visually appealing, and user friendly format for an information based site with hundreds of pages of content that doesn't have to rely on a server. By that I mean all but the external advertising can be viewed straight off a flash drive. No MySQL or PHP needed.
Here's some of the issues I've encountered:
The objection to orphaned pages can be easily handled with JavaScript.
The objection regarding bookmarking is irrelevant unless you use no frames all.
Content specific bookmarking can be handled with an "Add Bookmark" JavaScript function
The objection regarding SEO is easily handled by an XML sitemap and JavaScript.
Laying out dynamically sized frames is far easier and more dependable with standard framesets.
Targeting and replacing nested framesets from an external frame is easier with standard framesets.
In-house scripts like JavaScript searches and non-server dependent shopping carts that are too complex for cookies don't seem possible with iFrames, or if they are, it's way more hassle to get them working than using standard frames.
All that being said, I like the single page appeal of iFrames, and when they can actually do all the same stuff for my site as easily as standard frames does now, then I'll migrate. In the meantime, this nonsense about them being "obsolete" is as irksome as the other so-called "upgrades" they've foisted on us over the years without thinking it all the way through.
So what does all this boil down to for the question of whether or not to use framesets? The answer is that it all depends on what you want your site to do and on what platform it will mostly be viewed on. At some point it becomes impractical to make a multi-page site work well without some frames or iFrame integration. However if you're just creating a basic profile page that displays well on a cell phone or tablet, don't bother with framesets.
They almost always make people angry. What more do you need?
Frames are really useful in some occasions. If you are creating a local webpage that serves only for reading, no interactivity involved and the website will not be public on the internet, all the reasons on not to use frames are removed. For example a user manual for an application that is developed solely in html, frames are really useful in keeping a table of contents on the left in a simple and easy to code way. Also if you have proper navigation within the website then the back button ambiguity is removed completely
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Somewhere along the line I picked up the notion that using iframes is 'bad practice'.
Is this true? What are the pros/cons of using them?
As with all technologies, it has its ups and downs. If you are using an iframe to get around a properly developed site, then of course it is bad practice. However sometimes an iframe is acceptable.
One of the main problems with an iframe has to do with bookmarks and navigation. If you are using it to simply embed a page inside your content, I think that is fine. That is what an iframe is for.
However I've seen iframes abused as well. It should never be used as an integral part of your site, but as a piece of content within a site.
Usually, if you can do it without an iframe, that is a better option. I'm sure others here may have more information or more specific examples, it all comes down to the problem you are trying to solve.
With that said, if you are limited to HTML and have no access to a backend like PHP or ASP.NET etc, sometimes an iframe is your only option.
They're not bad practice, they're just another tool and they add flexibility.
For use as a standard page element... they're good, because they're a simple and reliable way to separate content onto several pages. Especially for user-generated content, it may be useful to "sandbox" internal pages into an iframe so poor markup doesn't affect the main page. The downside is that if you introduce multiple layers of scrolling (one for the browser, one for the iframe) your users will get frustrated. Like adzm said, you don't want to use an iframe for primary navigation, but think about them as a text/markup equivalent to the way a video or another media file would be embedded.
For scripting background events, the choice is generally between a hidden iframe and XmlHttpRequest to load content for the current page. The difference there is that an iframe generates a page load, so you can move back and forward in browser cache with most browsers. Notice that Google, who uses XmlHttpRequest all over the place, also uses iframes in certain cases to allow a user to move back and forward in browser history.
It's 'bad practice' to use them without understanding their drawbacks. Adzm's post sums them up very well.
On the flipside, gmail makes heavy use of iFrames in the background for some of it's cooler features (like the automatic file upload). If you're aware of the limitations of iFrames I don't believe you should feel any compunction about using them.
Having worked with them in many circumstances, I've really come to think that iframe's are the web programming equivalent of the goto statement. That is, something to be generally avoided. Within a site they can be somewhat useful. However, cross-site, they are almost always a bad idea for anything but the simplest of content.
Consider the possibilities ... if used for parameterized content, they've created an interface. And in a professional site, that interface requires an SLA and version management - which are almost always ignored in rush to get online.
If used for active content - frames that host script - then there are the (different) cross domain script restrictions. Some can be hacked, but rarely consistently. And if your framed content has a need to be interactive, it will struggle to do so beyond the frame.
If used with licensed content, then the participating sites are burdened by the need to move entitlement information out of band between the hosts.
So, although, occaisionally useful within a site, they are rather unsuited to mashups. You're far better looking at real portals and portlets. Worse, they are a darling of every web amateur - many a tech manager has siezed on them as a solution to many problems. In fact, they create more.
Based on my experience a positive side for iframe are when calling third party codes, that may involve calling a javascript that calls a has a Document.write(); command. As you may know, these commands cannot be called asynchronously due to how it is parsed (DOM Parser etc). An example of this is http://sourceforge.net/projects/phpadsnew/ I've made use of iframes to help speed up our site as there were multiple calls to phpadsnews and the site was waiting for the response before proceeding to render different parts of the page. with an iframe I was able to allow the site to render other parts of the page and still call the Document.write() command of phpads asynchronously. Preventing and js locking.
There are definitely uses for iframes folks. How else would you put the weather networks widget on your page? The only other way is to grab their XML and parse it, but then of course you need conditions to throw up the pertenant weather graphics... not really worth it, but way cleaner if you have the time.
The original frameset model (Frameset and Frame-elements) were very bad from a usability standpoint. IFrame vas a later invention which didn't have as many problems as the original frameset model, but it does have its drawback.
If you allow the user to navigate inside the IFrame, then links and bookmarks will not work as expected (because you bookmark the URL of the outer page, but not the URL of the iframe).
It's worth noting that iframes will, regardless of the speed of your users' internet connection or the contents of the iframe, cause a small (0.3s or so) but noticeable slowdown in the speed your page downloads. This is not something you'll see when testing it locally. Actually, this is true for any element added to a page, but iframes seem to be worse.
When your main page loads in HTTP protocol and parts of your page need to work in HTTPS protocol, iFrame can beat jsonp hands down.
Especially, if your dataType is not natively json and needs to be translated on server into json and translated on client back into e.g. complex html.
So nope - iFrame is not evil.
They are not bad, but actually helpful. I had a huge problem some time ago where I had to embed my twitter feed and it just wouldn't let md do it on the same page, so I set it on a different page, and put it in as an iframe.
They are also good because all browsers (and phone browsers) support them. They can not be considered a bad practice, as long as you use them correctly.
I have seen IFRAMEs applied very successfully as an easy way to make dynamic context menus, but the target audience of that web-app was only Internet Explorer users.
I would say that it all depends on your requirements. If you wish to make sure your page works equally well on every browser, avoid IFRAMEs. If you are targeting a narrow and well-known audience (eg. on the local Intranet) and you see a benefit in using IFRAMEs then I would say it's OK to do so.