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How can I change CSS variable on button click?

How can I make CSS change the button's box-shadow from var('--out') to var('--in') on button click, and when you click it again it'll change back to --out?

I tried doing it but whenever I click the button it just removes the whole shadow.

HTML + JS:

<body>
<section>
<button class="color_1">

</button>

<script>
    const btn = document.querySelector('button')
    const state = '--out'
    btn.addEventListener('click', _ =>{
        document.documentElement.style.setProperty(state, '--in')
    })
</script>

</section>
</body>

CSS:

:root{
    --in: inset 25px 25px 60px rgba(0,0,0,.5);
    --out: inset -25px -25px 60px rgba(0,0,0,.5);
}
.color_1{
    background-color: blue;
    border-radius: 200px;
    height: 300px;
    width: 300px;
    box-shadow: var(--out);
}
about 4 years ago · Juan Pablo Isaza
3 answers
Answer question

0

You need to use the :root selector with document.querySelector instead of document.documentElement to change the css variable. You also need to change the css to use a new --state variable that you can toggle between --in and --out with the JS code. You will also need to use getProperty to get the value of the --in or --out css variable before changing it. The following code in the script tag should fix your problem:

const btn = document.querySelector('button')
const state = '--in'
btn.addEventListener('click', _ =>{
    var root = document.querySelector(":root")
    root.style.setProperty("--state", root.style.getProperty(state))
})

And also using the following in your style tag:

:root{
    --in: inset 25px 25px 60px rgba(0,0,0,.5);
    --out: inset -25px -25px 60px rgba(0,0,0,.5);
    --state: var(--out);
}
.color_1{
    background-color: blue;
    border-radius: 200px;
    height: 300px;
    width: 300px;
    box-shadow: var(--state);
}
about 4 years ago · Juan Pablo Isaza Report

0

You are trying to change the value of one variable with another variable.

You will need getComputedStlye():

:root{
    --in: inset 25px 25px 60px red;
    --out: inset -25px -25px 60px green;
}
.color_1{
    background-color: blue;
    border-radius: 200px;
    height: 300px;
    width: 300px;
    box-shadow: var(--out);
}
<body>
<section>
<button class="color_1">

</button>

<script>
    const btn = document.querySelector('button')
    const state = '--out'
    btn.addEventListener('click', _ =>{  document.documentElement.style.setProperty(state, getComputedStyle(document.documentElement).getPropertyValue('--in'));
    });
</script>

</section>
</body>

But the ideal way would not be to change the value of your root variable. What if you need that value somewhere else. You can have separate classes for this on your element, which you add/toggle on a conditional basis.

:root{
    --in: inset 25px 25px 60px red;
    --out: inset -25px -25px 60px green;
}
.color_1{
    background-color: blue;
    border-radius: 200px;
    height: 300px;
    width: 300px;
}

.shadow1{
    box-shadow: var(--out);
}
.shadow2{
    box-shadow: var(--in);
}
<body>
<section>
<button class="color_1 shadow1">

</button>

<script>
    const btn = document.querySelector('button')
    const state = '--out'
    btn.addEventListener('click', function() {
    //this.classList.remove('shadow1');
    this.classList.toggle('shadow2');
    });
</script>

</section>
</body>

about 4 years ago · Juan Pablo Isaza Report

0

Ok here's what I got for you!

  1. It was removing --out value and setting it to --in looked like this (--out: --in;). Which is why we were seeing the box-shadow being removed

  2. This code: document.documentElement - was not targeting your button background - change it to: btn.style.boxShadow

const btn = document.querySelector('button');
   const state = '--out'
   btn.addEventListener('click', _ =>{
       document.documentElement.style.boxShadow = 'var(--in)';
   })
about 4 years ago · Juan Pablo Isaza Report
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