Eugene Karataev

Posted on Apr 23, 2019 • Edited on Jul 6, 2019

Javascript Set CSS Set CSS styles with javascript

#css #javascript #cssom

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';

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);

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.

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!

Top comments (14)

Ardalan • Jun 1 '20 • Edited

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];

Eugene Karataev • Jun 1 '20

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')

Ardalan • Jun 1 '20

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

yellow1912 • Jun 28 '20

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.

freq32 • Jun 24 '19

3 veeery interesting. thanks for the tip ;)

Jooyoung Moon • Jun 8 '20

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

But how it differ?

Eugene Karataev • Jun 8 '20

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.

marcin93 • May 26 '20 • Edited

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

Ardalan • Aug 16 '19 • Edited

really great post i like it

Ardalan • Jun 1 '20

great

xgqfrms • Sep 4 '20

developers.google.com/web/updates/...

xgqfrms • Sep 4 '20

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;
        }
      }
    `;