How to select and manipulate CSS pseudo-elements such as ::before and ::after using jQuery?

You could also pass the content to the pseudo element with a data attribute and then use jQuery to manipulate that:

In HTML:

<span>foo</span>

In jQuery:

$('span').hover(function(){
    $(this).attr('data-content','bar');
});

In CSS:

span:after {
    content: attr(data-content) ' any other text you may want';
}

If you want to prevent the 'other text' from showing up, you could combine this with seucolega's solution like this:

In HTML:

<span>foo</span>

In jQuery:

$('span').hover(function(){
    $(this).addClass('change').attr('data-content','bar');
});

In CSS:

span.change:after {
    content: attr(data-content) ' any other text you may want';
}

You'd think this would be a simple question to answer, with everything else that jQuery can do. Unfortunately, the problem comes down to a technical issue: css :after and :before rules aren't part of the DOM, and therefore can't be altered using jQuery's DOM methods.

There are ways to manipulate these elements using JavaScript and/or CSS workarounds; which one you use depends on your exact requirements.


I'm going to start with what's widely considered the "best" approach:

1) Add/remove a predetermined class

In this approach, you've already created a class in your CSS with a different :after or :before style. Place this "new" class later in your stylesheet to make sure it overrides:

p:before {
    content: "foo";
}
p.special:before {
    content: "bar";
}

Then you can easily add or remove this class using jQuery (or vanilla JavaScript):

$('p').on('click', function() {
    $(this).toggleClass('special');
});
p:before {
  content: "foo";
  color: red;
  cursor: pointer;
}
p.special:before {
  content: "bar";
}
<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.11.1/jquery.min.js"></script>

<p>This is a paragraph.</p>
<p>This is another paragraph.</p>
  • Pros: Easy to implement with jQuery; quickly alters multiple styles at once; enforces separation of concerns (isolating your CSS and JS from your HTML)
  • Cons: CSS must be pre-written, so the content of :before or :after isn't completely dynamic

2) Add new styles directly to the document's stylesheet

It's possible to use JavaScript to add styles directly to the document stylesheet, including :after and :before styles. jQuery doesn't provide a convenient shortcut, but fortunately the JS isn't that complicated:

var str = "bar";
document.styleSheets[0].addRule('p.special:before','content: "'+str+'";');
p:before {
  content: "foo";
  color: red;
}
<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.11.1/jquery.min.js"></script>

<p class="special">This is a paragraph</p>
<p>This is another paragraph</p>

.addRule() and the related .insertRule() methods are fairly well-supported today.

As a variation, you can also use jQuery to add an entirely new stylesheet to the document, but the necessary code isn't any cleaner:

var str = "bar";
$('<style>p.special:before{content:"'+str+'"}</style>').appendTo('head');
p:before {
  content: "foo";
  color: red;
}
<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.11.1/jquery.min.js"></script>

<p class="special">This is a paragraph</p>
<p>This is another paragraph</p>

If we're talking about "manipulating" the values, not just adding to them, we can also read the existing :after or :before styles using a different approach:

var str = window.getComputedStyle($('p')[0], ':before').getPropertyValue('content');
console.log(str);

document.styleSheets[0].addRule('p.special:before', 'content: "' + str+str + '";');
p:before {
    content:"foo";
    color: red;
}
<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.11.1/jquery.min.js"></script>

<p class="special">This is a paragraph</p>
<p>This is another paragraph</p>

We can replace document.querySelector('p') with $('p')[0] when using jQuery, for slightly shorter code.

  • Pros: any string can be dynamically inserted into the style
  • Cons: original styles aren't altered, just overridden; repeated (ab)use can make the DOM grow arbitrarily large

3) Alter a different DOM attribute

You can also to use attr() in your CSS to read a particular DOM attribute. (If a browser supports :before, it supports attr() as well.) By combining this with content: in some carefully-prepared CSS, we can change the content (but not other properties, like margin or color) of :before and :after dynamically:

p:before {
    content: attr(data-before);
    color: red;
    cursor: pointer;
}

JS:

$('p').on('click', function () {
    $(this).attr('data-before','bar');
});
p:before {
    content: attr(data-before);
    color: red;
    cursor: pointer;
}
<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.11.1/jquery.min.js"></script>

<p>This is a paragraph.</p>
<p>This is another paragraph.</p>

This can be combined with the second technique if the CSS can't be prepared ahead of time:

var str = "bar";

document.styleSheets[0].addRule('p:before', 'content: attr(data-before);');

$('p').on('click', function () {
    $(this).attr('data-before', str);
});
p:before {
  content: "foo";
  color: red;
  cursor: pointer;
}
<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.11.1/jquery.min.js"></script>

<p>This is a paragraph.</p>
<p>This is another paragraph.</p>
  • Pros: Doesn't create endless extra styles
  • Cons: attr in CSS can only apply to content strings, not URLs or RGB colors