Selecting and manipulating CSS pseudo-elements suc

Question

Is there any way to select/manipulate CSS pseudo-elements such as ::before and ::after (and the old version with one semi-colon) using jQuery?

For example, my stylesheet has the following rule:

.span::after{ content:'foo' }

How can I change 'foo' to 'bar' using jQuery?

Answer 1

In the line of what Christian suggests, you could also do:

$('head').append("<style>.span::after{ content:'bar' }</style>");

Answer 2

Here is the way to access :after and :before style properties, defined in css:

// Get the color value of .element:before
var color = window.getComputedStyle(
    document.querySelector('.element'), ':before'
).getPropertyValue('color');

// Get the content value of .element:before
var content = window.getComputedStyle(
    document.querySelector('.element'), ':before'
).getPropertyValue('content');

Answer 3

Someone else commented on appending to the head element with a full style element and that's not bad if you're only doing it once but if you need to reset it more than once you'll end up with a ton of style elements. So to prevent that I created a blank style element in the head with an id and replace the innerHTML of it like this:

<style id="pseudo"></style>

Then the JavaScript would look like this:

var pseudo = document.getElementById("pseudo");

function setHeight() {
    let height = document.getElementById("container").clientHeight;
    pseudo.innerHTML = `.class:before { height: ${height}px; }`
}

setHeight()

Now in my case I needed this to set the height of a before element based on the height of another and it will change on resize so using this I can run setHeight() every time the window is resized and it will replace the <style> properly.

Hope that helps someone who was stuck trying to do the same thing.

Answer 4

We can also rely on CSS custom properties (variables) in order to manipulate pseudo-element. We can read in the specification that:

Custom properties are ordinary properties, so they can be declared on any element, are resolved with the normal inheritance and cascade rules, can be made conditional with @media and other conditional rules, can be used in HTML’s style attribute, can be read or set using the CSSOM, etc.

Considering this, the idea is to define the custom property within the element and the pseudo-element will simply inherit it; thus we can easily modify it.

^{Please note that CSS variables might not be available in all browsers you consider relevant (e.g. IE 11): https://caniuse.com/#feat=css-variables}

1) Using inline style:

.box:before {
  content:"I am a before element";
  color:var(--color, red);
  font-size:25px;
}

<div class="box"></div>
<div class="box" style="--color:blue"></div>
<div class="box" style="--color:black"></div>
<div class="box" style="--color:#f0f"></div>

2) Using CSS and classes

.box:before {
  content:"I am a before element";
  color:var(--color, red);
  font-size:25px;
}

.blue {
  --color:blue;
}
.black {
  --color:black;
}

<div class="box"></div>
<div class="box black" ></div>
<div class="box blue"></div>

3) Using javascript

document.querySelectorAll('.box')[0].style.setProperty("--color", "blue");
document.querySelectorAll('.box')[1].style.setProperty("--color", "#f0f");

.box:before {
  content:"I am a before element";
  color:var(--color, red);
  font-size:25px;
}

<div class="box"></div>
<div class="box"></div>
<div class="box"></div>

4) Using jQuery

$('.box').eq(0).css("--color", "blue");
/* the css() function with custom properties works only with a jQuery vesion >= 3.x
   with older version we can use style attribute to set the value. Simply pay
   attention if you already have inline style defined! 
*/
$('.box').eq(1).attr("style","--color:#f0f");

.box:before {
  content:"I am a before element";
  color:var(--color, red);
  font-size:25px;
}

<script src="https://code.jquery.com/jquery-3.3.1.min.js"></script>
<div class="box"></div>
<div class="box"></div>
<div class="box"></div>

---

It can also be used with complex values:

.box {
  --c:"content";
  --b:linear-gradient(red,blue);
  --s:20px;
  --p:0 15px;
}

.box:before {
  content: var(--c);
  background:var(--b);
  color:#fff;
  font-size: calc(2 * var(--s) + 5px);
  padding:var(--p);
}

<div class="box"></div>

Answer 5

I'm always adding my own utils function, which looks like this.

function setPseudoElContent(selector, value) {    
    document.styleSheets[0].addRule(selector, 'content: "' + value + '";');
}

setPseudoElContent('.class::after', 'Hello World!');

or make use of ES6 Features:

const setPseudoElContent = (selector, value) => {    
    document.styleSheets[0].addRule(selector, `content: "${value}";`);
}

setPseudoElContent('.class::after', 'Hello World!');

Answer 6

There are many answers here but no answer helps to manipulate the css of :before or :after , not even the accepted one.

Here is how I propose to do it. Lets suppose your HTML is like this:

<div id="something">Test</div>

And then you are setting its :before in CSS and designing it like:

#something:before{
   content:"1st";
   font-size:20px;
   color:red;
}
#something{
  content:'1st';
}

Please notice I also set content attribute in element itself so that you can take it out easily later. Now there is a button clicking on which, you want to change the color of :before to green and its font-size to 30px. You can achieve that as follows:

Define a css with your required style on some class .activeS :

.activeS:before{
   color:green !important;
   font-size:30px !important;
 }

Now you can change :before style by adding the class to your :before element as follows:

<button id="changeBefore">Change</button>
<script>
    $('#changeBefore').click(function(){
        $('#something').addClass('activeS');
    });
</script>

If you just want to get content of :before, it can be done as:

<button id="getContent">Get Content</button>
<script>
    $('#getContent').click(function(){
        console.log($('#something').css('content'));//will print '1st'
    });
</script>

Ultimately if you want to dynamically change :before content by jQuery, You can achieve that as follows:

<button id="changeBefore">Change</button>
<script>
    var newValue = '22';//coming from somewhere
    var add = '<style>#something:before{content:"'+newValue+'"!important;}</style>';
    $('#changeBefore').click(function(){
        $('body').append(add);
    });
</script>

Clicking on above "changeBefore" button will change :before content of #something into '22' which is a dynamic value.

I hope it helps