84

Is there a way to change the properties of a CSS class, not the element properties, using jQuery?

This is a practical example:

I have a div with class red

.red {background: red;}

I want to change class red background property, not elements that have class red background assigned.

If I do it with jQuery .css() method:

$('.red').css('background','green');

it will affect the elements that right now have class red. Up to here everything is fine. But if I make an Ajax call, and insert more divs with red class, those won't have a green background, they will have the initial red background.

I could call jQuery .css() method again. But I would like to know if there is a way to change the class itself. Please consider this is just a basic example.

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4
  • 5
    I don't believe you can change the actual classes with jQuery. Commented Jul 13, 2012 at 16:23
  • 1
    I concur with Andrew Peacock, I know of no way to modify the actual css once loaded. However it seems trivial to perform update (changing the background from red to green) after changing an elements class. Commented Jul 13, 2012 at 16:30
  • You may be able to manipulate the <style> element. See CSSStyleSheet.deleteRule and CSSStyleSheet.insertRule Commented Mar 23, 2017 at 0:37
  • Another use case, in fact the one that brought me here, is to resize a popup window (actually, a series of DIV) according to the viewport, without using JS but just by assigning a certain class and then changing the class definition. Commented Jul 1, 2019 at 16:01

8 Answers 8

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52

You can't change CSS properties directly with jQuery. But you can achieve the same effect in at least two ways.

Dynamically Load CSS from a File

function updateStyleSheet(filename) {
    newstylesheet = "style_" + filename + ".css";

    if ($("#dynamic_css").length == 0) {
        $("head").append("<link>")
        css = $("head").children(":last");

        css.attr({
          id: "dynamic_css",
          rel:  "stylesheet",
          type: "text/css",
          href: newstylesheet
        });
    } else {
        $("#dynamic_css").attr("href",newstylesheet);
    }
}

The example above is copied from:

Dynamically Add a Style Element

$("head").append('<style type="text/css"></style>');
var newStyleElement = $("head").children(':last');
newStyleElement.html('.red{background:green;}');

The example code is copied from this JSFiddle fiddle originally referenced by Alvaro in their comment.

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3 Comments

even shorter: $("head").append('<style id="style_changer" type="text/css"></style>'); and later in code: $('#style_changer').html('.red{background:green;}');
This solution "Dynamically Add a Style Element" was perfect to me. Thank you! And @Tertium upgrade was even better.
One liner for the 2nd part: $("head").append('<style type="text/css">.red{background:green;}</style>'); Thanks, @Tertium
21

In case you cannot use different stylesheet by dynamically loading it, you can use this function to modify CSS class. Hope it helps you...

function changeCss(className, classValue) {
    // we need invisible container to store additional css definitions
    var cssMainContainer = $('#css-modifier-container');
    if (cssMainContainer.length == 0) {
        var cssMainContainer = $('<div id="css-modifier-container"></div>');
        cssMainContainer.hide();
        cssMainContainer.appendTo($('body'));
    }

    // and we need one div for each class
    classContainer = cssMainContainer.find('div[data-class="' + className + '"]');
    if (classContainer.length == 0) {
        classContainer = $('<div data-class="' + className + '"></div>');
        classContainer.appendTo(cssMainContainer);
    }

    // append additional style
    classContainer.html('<style>' + className + ' {' + classValue + '}</style>');
}

This function will take any class name and replace any previously set values with the new value. Note, you can add multiple values by passing the following into classValue: "background: blue; color:yellow".

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5 Comments

That's quite smart actually! You should include the code into your answer and remove the link ;)
Yes, please include the actual code, instead of linking (which can break and make this answer useless).
Okay, sorry for linking :)
There's nothing wrong with linking to the original source (and lots that's right) if you didn't write this code yourself.
Thanks! Excellent work. 2 tiny details from my IDE's syntax highlighter: 1. Remove var from var cssMainContainer = $('<div id="css-modifier-container"></div>'); 2. Add var to: classContainer = cssMainContainer.find('div[data-class="' + className + '"]');
11

You can remove classes and add classes dynamically

$(document).ready(function(){
    $('#div').removeClass('left').addClass('right');
});
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10

Didn't find the answer I wanted, so I solved it myself:
modify a container div!

<div class="rotation"> <!-- Set the container div's css -->
  <div class="content" id='content-1'>This div gets scaled on hover</div>
</div>

<!-- Since there is no parent here the transform doesnt have specificity! -->
<div class="rotation content" id='content-2'>This div does not</div>

css you want to persist after executing $target.css()

.content:hover {
    transform: scale(1.5);
}

modify content's containing div with css()

$(".rotation").css("transform", "rotate(" + degrees + "deg)");

Codepen example

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1 Comment

How well does this perform on a very large DOM? It seems any jQuery selector will take a long time since it has to sift through the large DOM...
2

$(document)[0].styleSheets[styleSheetIndex].insertRule(rule, lineIndex);

styleSheetIndex is the index value that corresponds to which order you loaded the file in the <head> (e.g. 0 is the first file, 1 is the next, etc. if there is only one CSS file, use 0).

rule is a text string CSS rule. Like this: "body { display:none; }".

lineIndex is the line number in that file. To get the last line number, use $(document)[0].styleSheets[styleSheetIndex].cssRules.length. Just console.log that styleSheet object, it's got some interesting properties/methods.

Because CSS is a "cascade", whatever rule you're trying to insert for that selector you can just append to the bottom of the CSS file and it will overwrite anything that was styled at page load.

In some browsers, after manipulating the CSS file, you have to force CSS to "redraw" by calling some pointless method in DOM JS like document.offsetHeight (it's abstracted up as a DOM property, not method, so don't use "()") -- simply adding that after your CSSOM manipulation forces the page to redraw in older browsers.

So here's an example:

var stylesheet = $(document)[0].styleSheets[0]; stylesheet.insertRule('body { display:none; }', stylesheet.cssRules.length);

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7 Comments

Hi ! A tiny -1 because I don't see the point of using $(document)[0] in place of document.
@PierreAntoineGuillaume Hi. document is wrapped in the jQuery/$ object because the person who asked the question specified how to do it using jQuery. $(element) is not the same thing as element - jQuery converts the wrapped element to a set element that has access to jQuery's methods. $(element)[0] is equivalent to $(element).get(0). This is explained in further detail at learn.jquery.com/using-jquery-core/jquery-object Happy moderating...
I didn't know of that, that's interesting. I can't remove the minus one if you don't edit, which kinda sucks
"jQuery also has a method named .get() which provides a related function. Instead of returning a jQuery-wrapped DOM element, it returns the DOM element itself. Alternatively, because the jQuery object is "array-like," it supports array subscripting via brackets: either case, firstHeadingElem contains the native DOM element.", so there is indeed no point in doing $(document)[0].styleSheets[styleSheetIndex].insertRule(rule, lineIndex); over document.styleSheets[styleSheetIndex].insertRule(rule, lineIndex);
I'd like to add the I found this to be the easiest way to get a particular style sheet $(`link[href="style.css"]`).prop("sheet"); It will always return the exact style sheet you want to edit, as the href/url are, ideally, always unique within a webpage Edit: though it will only work if the style sheet is loaded using <link>
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1

You can add a class to the parent of the red div, e.g. green-style

$('.red').parent().addClass('green-style');

then add style to the css

.green-style .red {
     background:green; 
}

so everytime you add red element under green-style, the background will be green

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Comments

0

Here's a bit of an improvement on the excellent answer provided by Mathew Wolf. This one appends the main container as a style tag to the head element and appends each new class to that style tag. a little more concise and I find it works well.

function changeCss(className, classValue) {
    var cssMainContainer = $('#css-modifier-container');

    if (cssMainContainer.length == 0) {
        var cssMainContainer = $('<style id="css-modifier-container"></style>');
        cssMainContainer.appendTo($('head'));
    }

    cssMainContainer.append(className + " {" + classValue + "}\n");
}
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1 Comment

As far as I can see, unlike this answer you are only appending and not replacing the values...
0

You may want to take a different approach: Instead of changing the css dynamically, predefine your styles in CSS the way you want them. Then use JQuery to add and remove styles from within Javascript. (see code from Ajmal)

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