I am using google's audit and its tells me to remove unused CSS. I don't know if that css is for just that page or the whole site. The CSS might be there but not needed on that page but another page. Can someone tell me how this works?
It is telling you to remove unneeded CSS for that page.
However you have rightly pointed out the flaw in this suggestion as it only takes into account the current page (in it's initial state, obviously if you have a pop-out menu it won't gather the CSS for that).
Think of it more as a guideline of making sure you don't send the whole of Bootstrap just for the grid and column layouts for example.
Overall this is very difficult to fix, just use the coverage section on the performance tab in Developer tools to make sure you don't have any massively bloated CSS files and you will be fine.
Obviously reduce your unused CSS if it is easy to do so.
The only other thing that this point covers (in it's description, not as part of it's monitoring) is deferring non-essential CSS.
You should defer any Style Sheets that are not required for rendering 'above the fold' content (and inline your 'above the fold' CSS).
This point is also covered in 'Eliminate Render Blocking Resources' so I never quite get why they add the suggestion under this part as well but I have added it for completeness.
I find this rule was good at guiding me when designing a theme from the ground up as it made me seperate global CSS and page CSS more effectively.
Unless your site is scoring 98 / 100 (or you have hundreds of kilobytes of CSS) and you want to squeeze that last little bit of performance out of the site, simply minify and combine your CSS files and ignore this point.
Google's audit tool compares the entire stylesheet against the current URL and then tells you how much of it is actually not used by the browser.
The browser however still needs to download the entire file and then match all CSS selectors that apply to the current URL.
There are many ways to deal with this, but I find it the easiest to use an external API tool like Splitcss that does this for you on URL basis.
If you have only a few URL patterns in your web application, you can use some CLI tools like purgecss or uncss.
Using a content script, I plan to insert a UI into the page in an <iframe>, but I have a few concerns.
Do people commonly use settings/extensions to block iframes on the page?
If my extension's iframe is blocked, is there a way for me to detect this?
Any other reasons to avoid the use of iframes in this scenario?
There are similar questions on the site, but they don't specifically ask what I want to know.
[The reason I want to use an iframe is this: My extension has to run independently of the website loaded (i.e. on any webpage). Its content script needs to show a UI for settings/help etc. Currently it does so by inserting a div into the page's DOM. However CSS from the webpage gets applied to the extension's UI, something which is harder to fix than one would think. Using an <iframe> seems to a way to avoid this issue.]
As you've discovered, trying to sandbox your CSS from interference, when injecting into the DOM is very difficult without declaratively setting every known style attribute. It's a well documented problem and some solutions can be found in the following posts:
How do I prevent CSS interference in an injected piece of HTML?
Is there a way to "sandbox" an HTML block away from its page's CSS without using iframes?
There's nothing fundamentally wrong with dropping your UI it into an <iframe>. I'm not aware of any settings or extension that would block this behaviour.
If your framed UI needs to interact with the DOM on the parent page or a content script you can do so with the use of Window.Parent. Also you may need to consider Same-Origin Policy if your pulling in the UI from another domain.
Answers in order:
People do not commonly use settings/extensions to block iFrames. Rather the opposite; the biggest complaint is how to get content out of iframes placed by ISP's and leach/wrapper sites, etc.
Yes, you can detect if your iFrame is blocked by having your iFrame's JS send an "I've started" message. If the message is not detected, assume the worst. :)
No reasons to avoid iFrames, other than they are a bit of a PITA to work with. If you just need to "show a UI for settings/help etc.", then it might be better to have your extension just open one of the popup window types available to extensions. You control the HTML/CSS/JS of those completely without worry of interference by the page.
I understand that frames are a lot more typing work to implement than Iframes, and that they require a lot more styling than Iframes. I am currently working on a website which must download some content (in fact, an entire set of webpages) from another website, one - by - one of course depending on the user's action on the main website. Iframes seem to be a short and rowdy way to implement this requirement, but what I am worried about is performance and integrity.
I would like some advice on what I would rather use when the following criteria is met:
The pages that must be downloaded onto my webpage are quite large (width and height)
Contains multiple images
Experiences occasional downtimes (maintainence)
any ideas for a man in wonder?
At this point, go with iFrames:
iFrame is HTML5. Frameset is obsolete in HTML5.
You have to load pages into each Frameset. iFrames can be embedded anywhere in a document.
You can style, hide, resize either, but iFrames are much easier to work with in this regard.
I've seen cases where the developer went with Frameset because he couldn't get the iFrame to size properly, but this isn't too big a deal with a little Javascript (if even that). The only reason to use a Frameset is if you don't fear it's eventual deprecation with modern browsers, and/or if you can't get iFrames to size the way you want based on the content you're integrating and need a quick solution.
If this is about display of 3rd party data in your site, you could use data feeds from the other sites if they're available, or use a screen scraper to extract the information you need, then display it in your own way on the page.
Unless it needs to look exactly like to other page.
Check out this link on screen scraping for ASP.NET
After working with many CMSes and cutting up many HTML designs, when I saw SilverStripe's use of CSS, I was converted.
Essentially, that it would be a waste to change IDs in <div> tags depending upon the page you were on, and that changing the <body> tag's classes and ID would be an easier way of changing specific pages.
Such convictions were brought into question by a coworker during the following problem:
On a specific website, we have a variety of pages that are similar in structure. Some may include a special form, and some may not. All special forms should have a different background image depending upon the sub-section we are in.
Due to a claim that "additional lines of CSS slow down body.onLoads," my argument to code all background expectations in the CSS was rejected.
Can anybody cite evidence between a variety of cases? Cases including: Badly-coded CSS, and CSS well-coded, but having a variety of unused CSS on each page?
(And specifically speaking on my problem, can anybody explain my unease? I feel uncomfortable assuming images will be there and auto-generating Inline CSS (or header-section-based style tags) based upon a variable from a database.)
It's not going to matter (noticeably) unless your website is Gmail or YouTube (or is similarly CSS heavy).
Google has some recommendations in their Page Speed guide:
http://code.google.com/speed/page-speed/docs/payload.html#RemoveUnusedCSS
Removing or deferring style rules that
are not used by a document avoid
downloads unnecessary bytes and allow
the browser to start rendering sooner.
Before a browser can begin to render a
web page, it must download and parse
any stylesheets that are required to
lay out the page. Even if a stylesheet
is in an external file that is cached,
rendering is blocked until the browser
loads the stylesheet from disk. In
addition, once the stylesheet is
loaded, the browser's CSS engine has
to evaluate every rule contained in
the file to see if the rule applies to
the current page. Often, many web
sites reuse the same external CSS file
for all of their pages, even if many
of the rules defined in it don't apply
to the current page.
The best way to
minimize the latency caused by
stylesheet loading and rendering time
is to cut down on the CSS footprint;
an obvious way to do this is to remove
or defer CSS rules that aren't
actually used by the current page.
Concerning this:
Due to a claim that "additional lines
of CSS slow down body.onLoads," my
argument to code all background
expectations in the CSS was rejected.
The extra time is in the order of a few milliseconds. Do what is easier and maintainable, not what is more "efficient".
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Closed 12 years ago.
For me iframes are pure evil (well, maybe not so pure). They seems to make a lot of troubles. Yes, your whole site will load once and then you can just load single pages. But people invented AJAX for this purpose.
One of the biggest issues I found with iframe was that I couldn't paste a link to one of the subpages, because the URL never changed (yes, I know there is a workaround for this). Second thing, web search engines may have problems indexing such pages.
Sometimes the accessibility of this sites are worse and some browser can even display them improperly.
There are better ways to design layouts without iframes. Everyday I can see some one asking at SO questions, like "How to access iframe with jQuery?".
So what are the benefits of iframes? What reason can it be to still use them? I just would like to know why.
I can think of 2 reasons (at the moment) why people would still use iframes instead of AJAX:
1) Iframes circumvent the cross domain origin policy (images, scripts, and styles do not). This can be useful for pulling in sites / content from other domain names relatively safely. Basically, this allows the advantage of being able to visually show data from other domains without letting them stomp all over your page with unlimited access (like something like JSONP would be able to do).
2) You can load multiple types of resources from within an iframe, not just certain mime-types (you're relatively limited to application/javascript, application/x-javascript, text/css, text/xml, image/png, image/jpeg, image/gif with scripts, XHR, images, and sources). For instance, if I want to show you a PDF, I can open an iframe and let the Adobe Reader plugin show you that file. Additionally, in the same domain, if I want to pipeline a script, style, and image all together (inline on the page, image would have to be data URI), I can accomplish this with an iframe (and if it's in the same domain, port, and protocol I can access it with JavaScript as well).
Did you know that Gmail is a set of iframes? The visible part is just clever positioning. Additionally, many OAuth implementation (Twitter, Facebook, Google, Yahoo!) usually use iframes to associate a user on their domain with a successful authentication URL (for after the user logs in).
IFRAMEs are used to embed and isolate third-party content into a website.
Most of web advertising solutions are based on iframes - because they give security (cross-domain policy) and isolated rectangle on screen which can be fully managed by third party content and scripting (a common use case is advertisments).
Another modern use of IFRAMES is a management of history (common back button workaround) of AJAX applications.
FRAMEs are poor version of IFRAMES. Their use is declining.
If a user has javascript disabled, iframes will work when ajax doesn't. This is not out of the question, considering that people use things like NoScript.
I use them on ajax websites, when I need to upload files without reloading the page.
I still see iframes being used in large corporations where they provide a single sign on which injects header information about the authenticated user which is then passed, via an iframe, towards the actual application(s). Since the "portal" surrounding the iframe handles all the specific authentication details those applications behind it don't need to have each an implementation for it, making things easier to make for the development team and having a single place to monitor and adjust authentication details of users.
There are plenty of technical reasons to use them (especially the security issue mentioned by Dan Beam).
What you shouldn't do is use iframes “like frames”, doing navigation to new pages by updating the iframe only. As you say, this prevents the navigation from being bookmarkable/linkable, responding to the normal navigation buttons, and providing useful link affordances like open-in-new-tab.
But that's not peculiar to iframes. You can see more and more pages where the navigation is done by fetching new content with XMLHttpRequest and writing it to the main content div's innerHTML. Often this is done with jQuery load() and clever-clever slidey animations. This breaks navigation just as badly as iframe-used-as-frame, or indeed old-school framesets. It's a shame so many web authors are using this tactic believing it to be a super-modern web design methodology, when really it's just a new skin on yesterday's despised framesets.
You can work around it in both cases, but it means you have to store a viewstate in the # fragment identifier part and support proper hash-navigation, which isn't trivial. Even then you've still got problems with non-JS agents like search engines; you end up having to have a parallel ?-based and #-based navigation to support both. It's a pain and most don't bother.
Framesets are outdated as of HTML 5, and sometimes you need to have a frame with another site within a site.
Also AJAX can only do so much. Try uploading a file to a site on another domain through https without an iframe. AJAX won't help you there.
In addition to others reasons, I have one specific usage of iframe in my application. Unfortunately, the target browser in my case is Internet Explorer 6. I need to have a footer and a header that are fixed in my web pages. The main part of this page is scrollable.
However, there is a bug in IE6 where I cannot display a div element on top of select elements using the z-index CSS property. Thus, I need to create an iframe that will be used as a hack to avoid this problem.
Of course, this is a really specific usage of iframe and only concern IE6...
Javascript WYSIWYG Editors use iframes, because that is easiest and best way to make it. For example TinyMCE uses it:
http://tinymce.moxiecode.com/
I was building a social network and i see iframes being useful for widgets to put on other peoples website to show like a mini profile or integrate with the content on a remote server. Seems like the most simple way to build this. I know some widgets use JavaScript. Also with the iframe method the session is the same as visiting the site like normal, so great for like buttons.
Many Formatted Text Editors (e.g. TinyMCE, HTMLArea) are implemented as iframe.
iFrames are okay for some cases, as X-domain-requests, or posting data to a source via parameters. But when I want to access data across domains, I prefer using CSS-files - they can accept params, set cookies, add content to the page (:before & :after) and give a visual feedback.