javascript - 如何确定 if::before 应用于元素？

Question

我有这个简单的 html 代码。我需要能够确定::before 是否应用于 .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>

我认为这会起作用，但它总是返回 0 的长度。

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

我错过了什么？

Answer 1

使用getComputedStyle 并检查content 的值。如果它是 none 则伪元素未定义:

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>

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

none

The pseudo-element is not generated. ^ref

如果你想简单地考虑一个过滤器:

const elems = document.querySelectorAll('div');
const divs = [...elems].filter(e => {
   var c = window.getComputedStyle(e,"before").getPropertyValue("content");
  return c != "none"
});

console.log(divs.length)

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

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

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