我在CSS中使用:root中定义的变量来修改:after(同样适用于:before)伪元素，特别是在下面使用JavaScript/jQuery生成随机颜色的演示中，更改由. slide -middle-out:hover:after定义的样式锚的背景颜色值和另一个锚(#reference)的内容值:

HTML

<a href="#" id="changeColor" class="sliding-middle-out" title="Generate a random color">Change link color</a>
<span id="log"></span>
<h6>
  <a href="https://stackoverflow.com/a/52360188/2149425" id="reference" class="sliding-middle-out" target="_blank" title="Stack Overflow topic">Reference</a>
</h6>
<script type="text/javascript" src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
<script type="text/javascript" src="https://cdn.rawgit.com/davidmerfield/randomColor/master/randomColor.js"></script>

CSS

:root {
    --anchorsFg: #0DAFA4;
}
a, a:visited, a:focus, a:active {
    text-decoration: none;
    color: var(--anchorsFg);
    outline: 0;
    font-style: italic;

    -webkit-transition: color 250ms ease-in-out;
    -moz-transition: color 250ms ease-in-out;
    -ms-transition: color 250ms ease-in-out;
    -o-transition: color 250ms ease-in-out;
    transition: color 250ms ease-in-out;
}
.sliding-middle-out {
    display: inline-block;
    position: relative;
    padding-bottom: 1px;
}
.sliding-middle-out:after {
    content: '';
    display: block;
    margin: auto;
    height: 1px;
    width: 0px;
    background-color: transparent;

    -webkit-transition: width 250ms ease-in-out, background-color 250ms ease-in-out;
    -moz-transition: width 250ms ease-in-out, background-color 250ms ease-in-out;
    -ms-transition: width 250ms ease-in-out, background-color 250ms ease-in-out;
    -o-transition: width 250ms ease-in-out, background-color 250ms ease-in-out;
    transition: width 250ms ease-in-out, background-color 250ms ease-in-out;
}
.sliding-middle-out:hover:after {
    width: 100%;
    background-color: var(--anchorsFg);
    outline: 0;
}
#reference {
  margin-top: 20px;
}
.sliding-middle-out:before {
  content: attr(data-content);
  display: attr(data-display);
}

JS / jQuery

var anchorsFg = randomColor();
$( ".sliding-middle-out" ).hover(function(){
    $( ":root" ).css({"--anchorsFg" : anchorsFg});
});

$( "#reference" ).hover(
 function(){
    $(this).attr("data-content", "Hello World!").attr("data-display", "block").html("");
 },
 function(){
    $(this).attr("data-content", "Reference").attr("data-display", "inline").html("");
 }
);

我总是添加我自己的utils函数，就像这样。

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

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

或使用ES6功能:

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

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

一种有效但不太有效的方法是在文档中添加带有新内容的规则，并用类引用它。根据需要，类可能需要为内容中的每个值提供唯一的id。

$("<style type='text/css'>span.id-after:after{content:bar;}</style>").appendTo($("head"));
$('span').addClass('id-after');

为什么要添加类或属性，当你可以添加一个样式头

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

在jQuery中不能选择伪元素，因为它们不是DOM的一部分。 但是你可以在父元素中添加一个特定的类，并在CSS中控制它的伪元素。

例子

jQuery:

<script type="text/javascript">
    $('span').addClass('change');
</script>

在CSS中:

span.change:after { content: 'bar' }

我在CSS中使用:root中定义的变量来修改:after(同样适用于:before)伪元素，特别是在下面使用JavaScript/jQuery生成随机颜色的演示中，更改由. slide -middle-out:hover:after定义的样式锚的背景颜色值和另一个锚(#reference)的内容值:

HTML

<a href="#" id="changeColor" class="sliding-middle-out" title="Generate a random color">Change link color</a>
<span id="log"></span>
<h6>
  <a href="https://stackoverflow.com/a/52360188/2149425" id="reference" class="sliding-middle-out" target="_blank" title="Stack Overflow topic">Reference</a>
</h6>
<script type="text/javascript" src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
<script type="text/javascript" src="https://cdn.rawgit.com/davidmerfield/randomColor/master/randomColor.js"></script>

CSS

:root {
    --anchorsFg: #0DAFA4;
}
a, a:visited, a:focus, a:active {
    text-decoration: none;
    color: var(--anchorsFg);
    outline: 0;
    font-style: italic;

    -webkit-transition: color 250ms ease-in-out;
    -moz-transition: color 250ms ease-in-out;
    -ms-transition: color 250ms ease-in-out;
    -o-transition: color 250ms ease-in-out;
    transition: color 250ms ease-in-out;
}
.sliding-middle-out {
    display: inline-block;
    position: relative;
    padding-bottom: 1px;
}
.sliding-middle-out:after {
    content: '';
    display: block;
    margin: auto;
    height: 1px;
    width: 0px;
    background-color: transparent;

    -webkit-transition: width 250ms ease-in-out, background-color 250ms ease-in-out;
    -moz-transition: width 250ms ease-in-out, background-color 250ms ease-in-out;
    -ms-transition: width 250ms ease-in-out, background-color 250ms ease-in-out;
    -o-transition: width 250ms ease-in-out, background-color 250ms ease-in-out;
    transition: width 250ms ease-in-out, background-color 250ms ease-in-out;
}
.sliding-middle-out:hover:after {
    width: 100%;
    background-color: var(--anchorsFg);
    outline: 0;
}
#reference {
  margin-top: 20px;
}
.sliding-middle-out:before {
  content: attr(data-content);
  display: attr(data-display);
}

JS / jQuery

var anchorsFg = randomColor();
$( ".sliding-middle-out" ).hover(function(){
    $( ":root" ).css({"--anchorsFg" : anchorsFg});
});

$( "#reference" ).hover(
 function(){
    $(this).attr("data-content", "Hello World!").attr("data-display", "block").html("");
 },
 function(){
    $(this).attr("data-content", "Reference").attr("data-display", "inline").html("");
 }
);