如何确定:: before是否应用于元素? [英] How to Determine if ::before is applied to an element?

问题描述

我有这个简单的html代码.我需要确定:: before是否已应用于.icon-player-flash

I have this simple html code. I need to be able to determine if the ::before is being applied to .icon-player-flash

    <div id="TestSwitch">

        <i class="icon-player-html5"></i>

        <i class="icon-player-none"></i>

        <i class="icon-player-flash"></i>

    </div>

我以为这行得通，但是长度总是返回0.

I thought this would work but it's always returning 0 for the length.

var flashplayer = $(".icon-player-flash:before");
console.log("count: " + flashplayer.length);

我想念什么?

推荐答案

使用getComputedStyle并检查content的值.如果它是none，则未定义伪元素:

Use getComputedStyle and check the value of content. If it's none then the pseudo element isn't defined:

var elem = document.querySelector(".box");
var c = window.getComputedStyle(elem,"before").getPropertyValue("content");
console.log(c);

var elem = document.querySelector(".alt");
var c = window.getComputedStyle(elem,"before").getPropertyValue("content");
console.log(c);

.box:before {
  content:"I am defined"
}

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

<div class="alt"></div>

此属性与:before和:after伪元素一起使用以在文档中生成内容.值具有以下含义:

This property is used with the :before and :after pseudo-elements to generate content in a document. Values have the following meanings:

无

未生成伪元素 . ^参考

The pseudo-element is not generated. ^ref

如果要计数:

console.log($('div').filter(function( ) {
    var elem = $(this).get(0);
    var c = window.getComputedStyle(elem,"before").getPropertyValue("content");
    return c != "none";
  }).length);

.box:before {
  content:"I am defined"
}

<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
<div class="box"></div>
<div class="box alt"></div>

<div class="alt"></div>
<div ></div>

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