Update CSS Module variables from Javascript

Question

I'm using a (now older) version of react-boilerplate which came with CSS Modules. What's nice about them is that you can create variables and import them in other CSS files.

Here's my colors.css file

:root {
  /* Status colors */
  --error: #842A2B;
  --success: #657C59;
  --pending: #666;
  --warning: #7E6939;
}

When I'm importing that file I just have to use at the top of my .css file:

@import 'components/App/colors.css';

I'm looking to have the option for two themes for my website and I would like to be able to dynamically update those variables with Javascript. What's the best way to do this?

Edit: I was hoping there's a way to update the colors.css file and not have to do conditional imports in all the components that draw from two possible css files... let me know if there's a way to do that and if there is I'll change the accepted answer. Thank you to all who answered!

Answer 1

I would just use the default color vars on the element/body/whatever, then put the alternate theme colors in another class, and toggle the theme class via JS. Here's a demo.

$("button").on("click", function() {
  $("body").toggleClass("foo");
});

body {
  --red: red;
  --blue: blue;
  --yellow: yellow;
  background: #ccc;
  text-align: center;
  font-size: 5em;
}

.foo {
  --red: #ce1126;
  --blue: #68bfe5;
  --yellow: #ffd100;
}

.red {
  color: var(--red);
}

.blue {
  color: var(--blue);
}

.yellow {
  color: var(--yellow);
}

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<span class="red">RED</span> <span class="blue">BLUE</span> <span class="yellow">YELLOW</span>
<br>
<button>click me</button>

Answer 2

I would have 2 sheets and conditionally switch between the two:

colours.scss

:root {
  /* Status colors */
  --error: #842A2B;
  --success: #657C59;
  --pending: #666;
  --warning: #7E6939;
}

otherColours.scss

:root {
  /* Status colors */
  --error: #FF0000;
  --success: #00FF00;
  --pending: #6666FF;
  --warning: #FF00FF;
}

then in your react code import them and use them as you wish:

import styles from 'colours.scss';
import alternativeStyles from 'otherColours.scss';

...

{this.props.useNormalStyle ? styles.myClass : alternativeStyles.myClass}

Answer 3

Is this what you are looking for?

      // get the inputs
      const inputs = [].slice.call(document.querySelectorAll('.controls input'));

      // listen for changes
      inputs.forEach(input => input.addEventListener('change', handleUpdate));
      inputs.forEach(input => input.addEventListener('mousemove', handleUpdate));

      function handleUpdate(e) {
        // append 'px' to the end of spacing and blur variables
        const suffix = (this.id === 'base' ? '' : 'px');
        document.documentElement.style.setProperty(`--${this.id}`, this.value + suffix);
      }

:root {
  --base: #ffc600;
  --spacing: 10px;
  --blur: 10px;
}

body {
  text-align: center;
}

img {
  padding: var(--spacing);
  background: var(--base);
  -webkit-filter: blur(var(--blur));
  /* 👴 */
  filter: blur(var(--blur));
}

.hl {
  color: var(--base);
}

/*
        misc styles, nothing to do with CSS variables
      */

body {
  background: #193549;
  color: white;
  font-family: 'helvetica neue', sans-serif;
  font-weight: 100;
  font-size: 50px;
}

.controls {
  margin-bottom: 50px;
}

a {
  color: var(--base);
  text-decoration: none;
}

input {
  width:100px;
}

<h2>Update CSS Variables with <span class='hl'>JS</span></h2>
<div class="controls">
  <label>Spacing:</label>
  <input type="range" id="spacing" min="10" max="200" value="10">

  <label>Blur:</label>
  <input type="range" id="blur" min="0" max="25" value="10">

  <label>Base Color</label>
  <input type="color" id="base" value="#ffc600">
</div>

<img src="http://unsplash.it/800/500?image=899">

<p class="love">😘</p>

<p class="love">Chrome 49+, Firefox 31+</p>