Develop Reference

How to test for css properties like modernizr.js

I would like to test if a browser supports a CSS property. I know I can use modernizr to do this but I don't want to install an entire library to test for one property.
How does modernizr test for properties? Say I want to test for support for the background-size property.
I scanned through the properties of the document object but couldn't see anything that looked like it would help.
Any ideas or help would be great.

Modernizr works by creating an element, applying a css property and then checking the return value of the css property. For example, if you wanted to test for text shadow you would do this:
if (document.createElement("detect").style.textShadow === "") {
document.getElementsByTagName("html")[0].className += " textshadow";
}

I think think this will be specific to each feature since you have to look for certain side effects in the DOM. Here is a link with some ideas http://www.sitepoint.com/detect-css3-property-browser-support/

Modernizr is an open source project - you can literally view the code that powers it. here is background-size detect specifically.
This is a fairly trivial thing to check. You create a dom element, set background-size (both vanilla and all of the vendor prefixed versions) to 100%, and then check the value of backgroundSize on the dom element's style property to see if it kept that value.
That being said - modernizr is pretty lean. You just get the tests you want, and nothing more.

Remove JavaScript styles, allowing CSS to take control

Preamble: Possible duplicate to my question can be found found here, although for me, this question was not sufficiently answered. A work-around is given, but a definitive answer to the question of whether or not it is possible, is not provided.
The question:
On my website, when a user clicks a button (or area of screen), I want that area to "flash" a couple of times before returning to its original state. (I think this gives the user a reassuring feel of something having been activated, as in some circumstances, they may have short delay before the feedback is given.)
Anyway, I've managed to get this working using a bit of JavaScript and jQuery, and you can see the results here >>.
As you may notice, the problem is that after the flashing is done, the element doesn't return to its original state. Rather, it keeps its last "flash" state, and overrides the underlying CSS styling which originally styles the object when the page loads.
I style the element with the following jQuery:
$jq_obj.css('background-color',flash_fg_color_).css('color',flash_bg_color_);
And I 'attempt' to un-style it with:
$jq_obj.removeAttr('background-color').removeAttr('color');
I've also tried:;
$jq_obj.css('background-color','').css('color','');
Despite the documentation saying that this should remove styling, it doesn't.
Is there a solution, or do I have to revert to the work-around solution referred to in my preamble? The nice thing about the JavaScript option is that it becomes a lot more versatile when you want to play around with the animations a bit.
Thanks,
===EDIT 2014-06-28===
As a demonstration of why the class solution is untidy, please see this fiddle: http://jsfiddle.net/Y9L4x/ (inspired by #BiffMaGriff 's proposed solutin here: http://jsfiddle.net/rte3G/)
The problem is that the elements being flashed could already be CSS-ed up to the hilt with multiple classes.
I recognise that I can remove styling classes first, before applying the "flash" classes, complicate the JavaScript and/or the CSS rules, etc. etc.
But the whole point of looking for a non-class-solution is that this option becomes extremely verbose in a real world situation, and you tend to have to program each flashing object individually, rather than the tidy one-JavaScript-function-fits-all that I'm searching for.

You are going to want to do your styles as classes.
.activated{
background-color: red; //or whatever else
}
and then with your jquery you can just toggle them a few times with the delays I assume you already have in your javascript.
$jq_obj.toggleClass('activated');

Try this:
$jq_obj.attr('style','');

The direct answer to the question appears to be a simple "No".
You cannot tell JavaScript to style an object, and then at a later stage, ask JavaScript to give styling responsibility back to CSS.
However, another messy work-around is to re-draw the HTML inside the element which contains your flashing-object.
$jq_flashing_obj.parent().html(original_html_);
This has the slight overhead of having to wrap your flashing object inside a div or span element, to ensure that the parent element contains nothing but your flashing element.
<div class="multiple-children">
link 1
<span class="wrapper">Click me to watch me flash</span>
link 3
</div>
You then, of course, have to capture the outerHTML of your flashing-object before the flashing starts.
original_html_ = $jq_obj[0].outerHTML;
The resulting JavaScript is a little bit verbose, as you see here: http://jsfiddle.net/CgsLs/ . However, it does have the following benefits:
Reusable on all clickable elements regardles of CSS :hover and other messy styling
Can optionally define the flash-color of the element inside the JS
Independent of CSS, meaning that the code is in one file, and therefore more maintainable
There are down-sides too
Requires the use of JQuery on() function (as opposed to simple click event handler)
Anyhoo... it may not be a solution for everyone. In some cases (maybe even most cases) the class option might be simpler.
But this is one other possible method of tackling this inherent shortcoming in JavaScript/Browser technology.

style.setProperty does not render

It seems like using this function would be more portable or reliable, because the alternative is to set an attribute:
element.style.setProperty(styleproperty, valuestring);
element.setAttribute('style',styleproperty+': '+valuestring+';');
The second method would also seem slightly more inefficient though that's hardly a concern.
But at least on Chrome, the style does not update on the page unless I use the setAttribute method.
The reason why this is a bit of an issue, is that I have potentially many different separate style properties I want to modify independently of the others. I have to do a whole lot of string parsing and processing if I can't make use of setProperty, removeProperty, etc. I have to pull out the style string, search it, modify it, and set it back in via setAttribute. Should work, but I don't like it.
Is there a reason for this? Is this a bug? My guess is that setAttribute triggers something for the browser to perform a re-render. What is a suitable way to force this update that is generally browser-friendly?

Setting the style attribute directly has consequences that may be undesirable: it will wipe out all existing styles set in the element's style attribute, and setAttribute is broken in older IE (and compatibility modes in later IE). Much safer is to use the element's style property directly to set only the style property you need:
element.style[styleproperty] = valuestring;
This will update the page immediately in all major browsers.
One caveat: CSS style properties (generally using dashes, such as in background-color) do not map precisely to properties of the DOM element's style object (generally camel case, such as in backgroundColor). There are also exceptions to this rule.

Is the only way to change a style to do it per-element in JavaScript?

I've been looking at a few different things I'd like to using JavaScript to tweak styles globally. I'd like to do this by changing the CSS rule that dictates the element's style (akin to doing this through the Inspector in Webkit), but after coming to https://developer.mozilla.org/en/DOM/CSSStyleRule I now don't know if this is even possible:
style
Returns the CSSStyleDeclaration object for the rule. Read only.
So, is there no way to change higher-level styles in JavaScript?

To modify your existing styles, either find the stylesheet in document.styleSheets or from the the .sheet property of the <style> or <link> element you want to modify. Then modify the properties in whatever rule they're located in (see https://developer.mozilla.org/en/DOM/CSSRuleList). I'd advice against using the CSSOM to modify properties, as browser support for modifying CSS properties through the CSSOM is pitiful (no browsers whatsoever support it). Instead, just set a string value.
If all you want to do is insert a new rule, just get a stylesheet from the method above, or document.documentElement.appendChild(document.createElementNS("http://www.w3.org/1999/xhtml","style")).sheet. Then use insertRule to add your rule.

CSS Styles can be created/changed programmatically via javascript, but that is not usually the easiest way to solve a problem because different browsers do it differently so cross-browser support is a bit of a pain unless you already have a library that abstracts that. You can see generally how to do it here: http://www.quirksmode.org/dom/changess.html.
If the styles you want to switch between are known in advance, then the easiest way to change between them is to define both those styles in a stylesheet, and use different class designations to trigger one vs. the other.
If you are just trying to affect one object or a small number of objects, you can simply add or remove a class name via javascript on the affected objects.
If there are large numbers of objects, then something I've done is to add a class name on the body tag to trigger the alternate style to take effect for all affected objects. It works like this:
Lots of these in your HTML:
<div class="foo"></div>
<div class="foo"></div>
<div class="foo"></div>
<div class="foo"></div>
Then, have two pre-defined CSS rules like this in this order:
.foo {background-color: #777;}
.alternate .foo {background-color: #F00;}
Then, using Javascript, any time you want to change to the alternate style, you simply do this (using jQuery or any favorite class library):
$(document.body).addClass("alternate");
To go back to the original style, you can just remove that class:
$(document.body).removeClass("alternate");
This doesn't have to be added to the body tag - it can be added to any common parent of all the affected objects.
I personally find this a lot simpler than programmatically creating style rules and it keeps the actual style information out of the code (where designer people who aren't programmers can more easily access it).
You can see this technique in action here: http://jsfiddle.net/jfriend00/UXKvg/

Overriding containers CSS behavior

I have created a Javascript based element that can be embedded into websites. The Javascript itself adds the HTML code into a pre-defined HTML container and dynamically loads the necessary CSS file that contain the element's visual definitions.
The problem starts when the site itself has its own definitions for general items. For example: The site's CSS defines a certain list style which is applied on the element's list because the element's CSS doesn't define an explicit list style or if the site's CSS overrides the element's CSS definition.
For the time being, I was able to solve this specific issue by explicitly defining the list's style and adding the !important definition. However, I would definitely want to go for a more robust solution that will assure that:
1. CSS definitions from the site's CSS that are not explicitly defined in the element's CSS will not be applied on the element
2. I will not need to explicitly add the !important definition to every one of my CSS definitions
Is there a general way in which I can specify that a site's CSS will not be applied on a certain element or that only a certain CSS will be applied to a specific element?
Any help will be greatly appreciated.

You need to use a localised reset.
Grab an existing CSS reset, such as Eric Meyer's Reset Reloaded and namespace all the selectors with your parent element, e.g. #something a { ... }.

I was going to put up the same answer as Alex, but he beat me - but I was also going to add:
If you're not going to use #alex's suggestion then ultimately you have to explicitly style all of your elements the way that you want them to appear; using selectors that keep your styles local too (and don't interfere with the parent site) - in the same way that the localised reset is suggested.
Update
Or you could do what Google Translate and many other widget-type things do, usually a no-no but in dynamic scenarios I think perfectly acceptable; since the visual style of your elements is not just important to you but to the container site: use inline styles.
Final update
So I thought I'd just double check what Google Translate does. And of course it's an iFrame inject in addition to using inline styles. They no doubt use inline styles to maximise compatibility and so that the browser doesn't have to make another request to get the stylesheet; and they would be using an iFrame so they can ensure a consistent look and feel.
Consider both of those points in tandem - and weigh that up against the amount of work that might be required in resettting all the styles for a minority portion of the page; or defining rules for every CSS property you need to control - which, let's face it, is basically all visual CSS properties.
The iFrame solution actually seems to offer the best solution - if you can use it; hence I've +1'd the first comment by #roberkules on your question.