设置完后，用Javascript替换"var" css属性 [英] Replace with Javascript the 'var' css property after it has been already set

问题描述

我有一个设置了var属性的元素，如下所示:

I've an element with a var property set on it like so:

 <div class="divwithbackground" style="--page-header-section-background: url('myurlimage.jpg');">
 </div>

CSS

 .divwithbackground::after {
     background-image: var(--page-header-section-background);
     background-position: center;
     background-size: cover;
 }

这实际上很好.但是，如果我还有另一个设置属性的javascript会怎么办:

This actually works well. But what if I have another javascript which sets the property:

document.documentElement.style.setProperty('--page-header-section-background', bgDataValue, 'important');

这样.好吧，如果我从DIV标签中删除了样式，这会起作用:

this way. Well this works if I remove style this from the DIV tag:

 style="--page-header-section-background: url('myurlimage.jpg');

但这不是我想要的行为.我想用javascript替换已经设置的属性.这可能吗?

But this is not the behavior I want. I would like javascript to replace the already set property. Is this possible ?

推荐答案

您需要定位元素本身以覆盖变量

You need to either target the element itself to override the variable

setTimeout(function() {
document.querySelector('.divwithbackground').style.setProperty('--b', 'linear-gradient(blue,blue)');
},1500);

.divwithbackground::after {
  content: "";
  display: block;
  height: 50px;
  background-image: var(--b);
}

<div class="divwithbackground" style="--b: linear-gradient(red,red);">
</div>

或者，如果要定位根元素，可以考虑使用一个备用技巧:

Or consider a fallback trick if you want to target the root element:

setTimeout(function() {
document.documentElement.style.setProperty('--b', 'linear-gradient(blue,blue)');
},1500);

.divwithbackground::after {
  content: "";
  display: block;
  height: 50px;
  background-image: var(--b,var(--c));
}

<div class="divwithbackground" style="--c: linear-gradient(red,red);">
</div>

您还可以根据需要设置/重置初始值:

You can also set/reset the initial value like you want:

function change() {
  document.documentElement.style.setProperty('--b', 'linear-gradient(blue,blue)');
}

function reset() {
  document.documentElement.style.setProperty('--b', 'initial');
}

.divwithbackground::after {
  content: "";
  display: block;
  height: 50px;
  background-image: var(--b, var(--c));
}

<div class="divwithbackground" style="--c: linear-gradient(red,red);">
</div>

<button onclick="change()">change</button>
<button onclick="reset()">reset</button>

相关问题/答案以获取更多详细信息:

Related questions/answers for more details:

如何在CSS自定义属性(又称为CSS变量)中存储继承值?

盒子模型的CSS自定义属性(变量)

用于在外部范围内计算变量时忽略了CSS范围的自定义属性

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