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Javascript Set CSS Set CSS styles with javascript

karataev profile image Eugene Karataev Updated on ・2 min read

Let's say you have a paragraph.

<p id="target">rainbow 🌈</p>

And you need to change it's color with JS. What options do you have?

1. Inline styles

The most straightforward path. Query the element from DOM and change it's inline styles.

document.getElementById('target').style.color = 'tomato';

inline styles

Short and simple.

2. Global styles

Another option is to create <style> tag, fill it with CSS rules and append the tag to the DOM.

  var style = document.createElement('style');
  style.innerHTML = `
  #target {
  color: blueviolet;
  }
  `;
  document.head.appendChild(style);

global styles

3. CSSOM insertRule

Third option is less known. We gonna use CSSStyleSheet insertRule method.

  var style = document.createElement('style');
  document.head.appendChild(style);
  style.sheet.insertRule('#target {color: darkseagreen}');

While it might look similar to the 2nd option, it's definitely different.
insertRule

As you can see in Chrome devtools, <style> tag is empty, but the style (darkseagreen color) is applied to the element. Also the color can't be changed via devtools because Chrome doesn't allow editing dynamic CSS styles.

Actually such behavior was the motivation to write this post. A popular CSS-in-JS library Styled Components use this feature to inject styles in production mode because of performance. This feature might be undesirable in specific projects or environments and some folks complain about it in the project's issues.

4. Constructable Stylesheets (July 2019 update)

It's now possible to create CSSStyleSheet object from JavaScript.

// Create our shared stylesheet:
const sheet = new CSSStyleSheet();
sheet.replaceSync('#target {color: darkseagreen}');

// Apply the stylesheet to a document:
document.adoptedStyleSheets = [sheet];

More details are here.
This option is only valid for Chrome, so use with caution.

Do you know other options to add styles with javascript? What is your preferred option these days?

Thanks for reading!

Discussion

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mzahraei profile image
Ardalan

hey can you maybe help me ?
I have some things like this and I just want to Update the hidden class but I Update Complete Style

<style id="style">
    .hidden{
         animation-name: bgshower;
        animation-duration: 2s;
        position: absolute;
        z-index: 2;
    }
    .neopa{
        background-color: darkred;
        font-size: large;
    }
</style>

var style = document.getElementById('style');
var counter = parseInt(60);

        style.innerHTML = `

        .bghidden {
            height: 100%;
            width: 100%;
            background-color: #E96565;
            top: 0;
            left: 0;
            `+ 'animation-duration:' + counter + "s" + `;

            animation-name: bgshower;
            animation-delay: 0s;

            position: absolute;
            z-index: 2;
        }
        `;
        document.adoptedStyleSheets = [style];
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karataev profile image
Eugene Karataev Author

I'm not 100% sure what you're trying to achieve, but if you need to add animations on an element(s) with JS after some event, consider the following way:

  • Define styles with css like
.hidden {
...
}

.animate {
...
}
  • Add/remove CSS classes with animations when necessary with DOM API: document.querySelectorAll('.hidden').classList.add('animate')
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mzahraei profile image
Ardalan

Thanks for writing but I just wanted to update an element's CSS with JS.
no more new class I wanted to Edit animation-duration value from JS.
I resolve it thx

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yellow1912 profile image
yellow1912

With CSSStyleSheet, what is the best way to replace a rule? I see insertRule seems to take an index, if I re-use that same index then that rule will be replaced? The reason is that I want to allow the endusers to change some styles via a UI, then quickly update that to the specific element.

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codemilli profile image
Jooyoung Moon

Hi :D
I just wondered if using insertRule for performance or not and I found this article. Thanks !

But how it differ?

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karataev profile image
Eugene Karataev Author

I don't think you ever need to use insertRule in your day-to-day job unless you hit some performance bottleneck when working with styles.
I think optimizations with insertRule are useful for libraries (like styled-components), but add unnecessary complexity when developing regular websites or apps.

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marlo22 profile image
marcin93

It's something I'm looking for. Thanks a lot!

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smz_68 profile image
Ardalan

really great post i like it

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freq32 profile image
freq32

3 veeery interesting. thanks for the tip ;)

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xgqfrms profile image
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xgqfrms profile image
xgqfrms

style.setContent bug ❌

    const style = document.createElement(`style`);
    // this.shadowRoot.appendChild(this.templateContent);
    // log(`this.shadowRoot`, this.shadowRoot);
    style.setContent = `
      .run {
        width: 100px;
        height: 100px;
        background: url(https://www.boston.com/wp-content/uploads/2016/05/yuge_anger.png) 0 0;
        animation: run 500 step(6) infinite;
      }
      @keyframes run {
        from {
          background-position: 0 0;
        }
        to {
          background-position: -600px 0;
        }
      }
    `;

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mzahraei profile image
Ardalan

great

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nagarjundeepak profile image
Nagarjun

this is really helpful :)