浏览器无法理解的CSS值将被丢弃，这说明了为什么-my-custom-property无法通过来获取CSS值.style。

过去，您不得不依靠存储具有数据属性的数据并自己通过JavaScript处理继承。

但是，自此以来，“自定义属性”（也称为“CSS变量”）已被引入标准并由浏览器实现，截止到2019-05-09，全球约有92％的支持。乍一看，Edge似乎是最后一个实现的主要浏览器，2017年10月16日发布了版本16。

本质上，您需要--my-custom-property:'foobar';在元素上设置自定义属性（例如），并且可以使用类似getComputedStyle(your_el).getPropertyValue("--my-custom-property")返回的内容'foobar'（带有前导空格）对其进行访问。请注意前导空格和引号。它将完全返回所提供的值。

例：

console.log(getComputedStyle(document.getElementById("a")).getPropertyValue("--my-custom-property-1"))

console.log(getComputedStyle(document.getElementById("b")).getPropertyValue("--my-custom-property-2"))


#b-div { --my-custom-property-2: 'world' }


<div style="--my-custom-property-1: 'hello'"><h1 id="a">#a 'hello'</h1></div>

<div id="b-div"><h1 id="b">#b 'world'</h1></div>

这是使用一个和两个前导连字符，继承以及检索值的不同方法进行的一些测试：

function log(computed, selector, prop, value) {

  let method = computed ? "getComputedStyle(el)" : "el.style"

  let method_id = computed ? "computed" : "raw"



  // Build first level of list (tag name)

  let first = document.querySelector("#" + selector)

  if (!first) {

    first = document.createElement("li")

    first.appendChild(document.createTextNode(selector))

    first.setAttribute("id", selector)

    first.appendChild(document.createElement("ul"))

    document.querySelector("ul").appendChild(first)

  }



  // Build second level of list (method of style retrieval)

  let second = document.querySelector("#" + selector + "-" + method_id)

  if (!second) {

    second = document.createElement("li")

    second.appendChild(document.createTextNode(method))

    second.setAttribute("id", selector + "-" + method_id)

    second.appendChild(document.createElement("ul"))

    first.querySelector("ul").appendChild(second)

  }



  // Build third level of list (property accessed)

  let third = document.querySelector("#" + selector + "-prop" + prop)

  if (!third) {

    third = document.createElement("li")

    third.appendChild(document.createTextNode(prop + ": `" + value + "`"))

    third.setAttribute("id", "prop" + prop)

    second.querySelector("ul").appendChild(third)

    if (value === "") {

      third.classList.add("bad")

    } else {

      third.classList.add("good")

    }

  }

}



// Uses .style

function getStyleAttr(selector, prop) {

  let value = document.querySelector(selector).style.getPropertyValue(prop)

  log(false, selector, prop, value)

}



// Uses getComputedStyle()

function getStyleComputed(selector, prop) {

  let value = getComputedStyle(document.querySelector(selector)).getPropertyValue(prop)

  log(true, selector, prop, value)

}



// Loop through each property for each element and output the value

let selectors = ["article", "h1", "p"]

let props = ["--my-custom-property", "-my-custom-property"]

selectors.forEach(function(selector) {

  props.forEach(function(prop) {

    getStyleAttr(selector, prop)

    getStyleComputed(selector, prop)

  })

})


code {

  background: #eee;

  padding: .2em;

}



.bad {

  color: #800;

}



.good {

  color: #080;

}


<article class="custom-prop-inheritance" style="--my-custom-property: 'foobar'; -my-custom-property: 'foobar'">

  <h1>Title</h1>

  <p>Custom properties require two leading hyphens (<code>-my-custom-property</code> <em>never</em> works). Using <code>el.style</code> does not support inheritance. To support both inheritance and custom properties, you must use <code>getComputedStyle(<b>el</b>)</code> along with two leading hyphens on the custom property (eg, <code>--my-custom-property</code>).</p>

</article>

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