Develop Reference

How to hide CSS background images that use !important

I'm trying to create a bookmarklet that will hide images on any page I'm currently viewing. It works for removing <img> tags and it creates a CSS style that tries to hide all background images. The issue I keep encountering are background images that are specified with !important. I can't figure out how to hide them.
Here is a codepen demonstrating the issue: http://codepen.io/Chevex/pen/kbDcv
If you remove the !important from the background image then it all works fine. Any ideas?

Make sure your CSS occurs after that CSS on the page and put the !important override on your CSS. Also, since you specify that you are using JavaScript, you can add your CSS as inline CSS on the actual element and use !important. The only thing that overrides inline important is user agent user important style sheets.[reference][example]

As others have pointed out, you can use the newer (IE9+) querySelectorAll function:
function hideImages() {
var d = document,s = window.getComputedStyle;
Array.prototype.forEach.call(
d.querySelectorAll("body *"),
function(el){
if (s(el).backgroundImage.match(/url/) ||
el.tagName === 'IMG'){
el.style.visibility="hidden";
}
}
);
}
$('button').click(hideImages);
http://codepen.io/anon/pen/rBnIx
Updated to include background-images set via CSS.
Though, you could probably lose a lot by turning anything with a background-image invisible. You might have better luck just turning that property off. You could either check the computed style of each element like above or just set them all like below. The function below uses setProperty to override !important which is also IE9+.
function hideImages() {
var a=document.querySelectorAll("body *"),i=a.length;
function _f(n){
if (n.tagName === 'IMG') n.style.visibility="hidden";
n.style.setProperty("background-image", "none", "important");
};
while(--i) _f(a[i]);
}
http://codepen.io/anon/pen/tnrdH

you can hide divs with backgrounds in the same manner as you do img tags in the linked code:
var imgs=document.querySelectorAll("div[style*='background']");
for (var i=0;i<imgs.length;i++) {
imgs[i].style.visibility="hidden";
}

jQuery to update actual CSS

First off: I'm aware of the jQuery.css() function, but it doesn't work in my case. I'll explain why.
I have a jQuery color picker being used to change the highlighting of a website. I want to apply that color picker to the border of an element which only shows on hover.
The jQuery.css() function only applies the CSS to elements it finds, and does not work on the :hover CSS attribute.
I've tried adding a CSS class which I toggle on the hover, but it comes back to the same problem: I'm trying to change ONLY the hover value.
There's got to be a way to do this, but I've been searching StackOverflow and Google for the better part of an hour now, so I'm invoking xkcd #627

Use the hover event to achieve the same results.
$('selector').hover( function(){
//A function to execute when the mouse pointer enters the element.
$(this).css('property','value');
}, function(){
//A function to execute when the mouse pointer leaves the element.
$(this).css('property','value');
});

I'm adding this as an alternative answer.
If you need to dynamically change your CSS then there is something wrong with your CSS. It's very strange that you need a definition, that you can't toggle with a class and has to be generated dynamically.
Let's say you have a widget that can be in two modes: inactive or active. When it's active elements in it should respond visually to a hover event, when it's not, they shouldn't.
<div id="my-widget" class="my-widget-container">
<div class="element">Something to look at</div>
</div>
CSS
.my-widget-container .element { background-color: #ffffff; }
.my-widget-container.active .element:hover { background-color: #00ff00; }
You switch the mode by:
$("#my-widget").addClass("active");
This will activate the :hover line for the element which now appears interactive.
If I knew more about your situation I could perhaps fix a fitting solution.
Also, jQuery.css is poorly named, perhaps jQuery.style would be a better name since that is exactly what it does.

jQuery - Selecting a child div background image and amending it

Im looking for a way to change the background image of a div using jQuery BUT only amending it, not totally changing it.
Let me explain.
Im using http://jqueryui.com/demos/sortable/#portlets to show some div's that open and close. Now when you click the portlet header it opens and closes the content below.
Inside the portlet header i have a child div which shows an arrow (either up or down) depending on the current state of the content. I need a way of changing the background image on this child div by adding on "-visible" onto the end of the url for the background image.
I wouldnt even know where to start with doing this, but i have added some code below for you to look at.
http://jsfiddle.net/45jZU/
From the fiddle there, i need to alter the background image of the portlet-arrow div inside portlet header. I can not simply change the background image all together, but i have simplified it down to post on here.
I hope this isnt too narrow to not be of use to anyone else on stackoverflow.
Thanks

Maybe I'm missing something here, but can't you use the .css attribute modifier for the selected jQuery object? Something like:
var current_background = $("#my-div").css("background-image");
$("#my-div").css("background-image", current_background + "-visible");
If you're looking to modify the class names themselves, you can try mess around with the .toggleClass(), .hasClass(), .addClass() and .removeClass() methods in jQuery.
I hope this helps, but let me know if I've missed the mark here completely!

I would personnaly go for using css classes to change the background image. If you decide to change the image afterwards, you won't have to alter your javascript. It is a better solution to use javascript to code the behavior of the widget, not the visual aspect.
So you have the following css:
.portlet-header {
background-image: url(<an image>);
}
.portlet-header.collapsed {
background-image: url(<an other one>);
}
Add this line to your javascript to toggle the collapsed class:
$(".portlet-header").click(function() {
...
$(this).parent().toggleClass('collapsed');
});
If you widgets starts collapsed, initially add the class.
DEMO

want to change color at multiple places in one go !

My problem is I have couple of divs in my page. All have header of similar color. Now if I have to change the color(for example background color) of all divs, I have to make changes as many divs I have. Is it not possible to just change or say write the color code at one place (like in a variable) and the then use that variable as color value in the embedded styles to all those divs. Something like javascript entities.

If you need variables in CSS, you might want to look at CSS pre-compilers (is this the correct term?), such as Sass, which does this Server-side and eases the pains for having many different color repeated across multiple rulesets.
Otherwise, when developing, try splitting your CSS files into individual components, such as typography.css, color.css etc. to help better organise them. You'll still want to combine them after development is complete for better performance, but doing this does help keep things neater and tidier.
Lastly, you can always define large rules like this:
#header, #footer, #nav, #sidebar {
color: orange; /* I like orange! */
}
Which would reduce redundancy somewhat. Using Javascript for styling and presentation should only be kept as a last resort; there are always tools available to keep your CSS tidy; you only need to use them.

u can write some css and jquery to achive this
.color1
{
color:red;
background-color:green;
}
.color2
{
color:blue;
background-color:orange;
}
now on some event u can change classes. for example intitially u have
<div class="header color1">SOME TEXT HERE</div>
<div class="header color1">another header</div>
u can change this with jquery or even with javascript :)
$("#somebutton").live("click", function(){
$(".header").removeClass('color1');
$(".header").addClass('color2');
});
this will change color of both headers at click of button with id somebutton

How about setting the same class on all divs and set all common colors in there? That way you'd only have to change the color for that class.

I would suggest using jQuery or another javascript library, to do this.
Assign a class to the divs you wish to alter, and then use the following code (when giving them a clas of 'header-div')
$('.header-div').('background-color','#FF0000');
this will change ALL elements with the class of 'header-div'

Jquery solution
define all the divs with a specific class like
<div class="changeable"></div>
Then use jquery to change the background
$(".change").click(function() {
$(".changeable").css("background","#000");
});

Quickly repaint array of unicode symbols in JavaScript

I want to change background/foreground color of many symbols with the same CSS class. Right now I'm doing it with jQuery — like $('back_COLORED').css('background-color', '#00FF00'), but this approach is slow when there are many elements with such class (>900).
Seems it's because jQuery don't change CSS rules itself, but finds all elements one-by-one and applies inline styles to them. At least, this is what I see in inspector. So, the question is:
How can I change the CSS rules itself?
Will it be much faster?
Can I make it cross-browser (IE6 doesn't count)?
UPD: I'm trying to make some kind of color scheme editor. The source is at http://github.com/kurokikaze/cinnabar/. Don't mind PHP things, editor is fully client-side (with just some libraries fetched from the net).
UPD2: Tried canvas approach, still slow. Canvas branch is at http://github.com/kurokikaze/cinnabar/tree/canvas.

The most cross-browser friendly way to override a class definition is to write a new rule and add it to the end of the last stylesheet in the document. You can edit an existing style rule, but even some recent browsers can make it difficult.
function newRule(selector, csstext){
var SS= document.styleSheets, S= SS[SS.length-1];
// this example assumes at least one style or link element
if(S.rules){
S.addRule(selector,csstext,S.rules.length);
}
else if(S.cssRules){
S.insertRule(selector+'{'+csstext+'}'),S.cssRules.length)
}
}
newRule('.someclass','background-color:#0f0');
You can add as many 'property:value;' bits in the csstext as you need.
Remember to prefix a '.' to a class name or a '#' to an id,
and the css must be written as a style rule (with-hyphens, not camelCase).
Of course, it will not override inline styles, and it is overkill for small, local changes.
It also may make the redrawing of the page more obvious than changing one element at a time,
but it may be just what you need here.

There are different ways depending on which browser you are dealing with. This is documented on Quirks Mode.
Some libraries provide an abstraction layer, such as YUI's StyleSheet utility.
There should be a significant performance boost since you aren't using JS/DOM to cycle through all the elements.
Another approach would be to predefine your styles:
body.foo .myElements { … }
And then edit document.body.className

If you can select the parent div by id, maybe you could select by tag inside it? Or are there elements of the same kind that should change color and that should not, inside the parent?
It would be nice to have an idea of what you're building here. 900+ objects seems to be a lot... maybe a completely different approach could be used? Canvas, SVG?

Try hiding the items you want to change before changing them, make the change and then display them again. This is common practice to speed up things as you minimize the repaint events in the viewport. In this case when you only setting one css property it might not be that of a benefit but it´s worth a try I say.
Try:
$('back_COLORED').hide();
$('back_COLORED').css('background-color', '#00FF00');
$('back_COLORED').show();
or
$('back_COLORED').hide().css('background-color', '#00FF00').show();

I would stick in trying changing a CSS property, instead of parsing the DOM.It is about the CSS engine vs. DOM+JS here, and the winner is clear.
It happens I just uploaded a tiny library that replaces CSS by Javascript: jstyle
This is may be an overkill, but you will find in the source code of jstyle.js all the code you need to update cross browser the CSS properties of your page.

I think a better solution would be to write a more specific CSS rule (that would override the normal colour) that can be activated by simply changing one element's css class.
So for example if you had the following structural markup:
<div id="container">
<span class="colored">Test 1</span>
<span class="colored">Test 2</span>
</div>
And CSS:-
.colored { background-color: red; }
.newcolor .colored { background-color: blue; }
Then in your jquery you add the .newcolor class to the container div:-
$('#container').addClass('.newcolor');
When you do that the second CSS rule will override the first because it is more specific.

Inject the css code into a style tag:
var style = $('style').attr({
type:"text/css",
media:"screen",
id:'changeStyle'
}).html('.tempClass { color:red } .tempClass p { background:blue }').prependTo('body');
and on every changes on your color with color picker you only rewrite the html inside of #changeStyle tag.
Have no idea if it works (didn't tested) but you should give a try.

This is jQuery pluggin for work with css rules: http://flesler.blogspot.com/2007/11/jqueryrule.html
not sure about its performance, but worth a try.