{Svelte} How to Dynamically Inject CSS Classes


1 min read

Hi, today I want to show you how I dynamically assign CSS classes to an HTML tag. I really like Svelte, but I miss the class bindings in VueJS https://vuejs.org/guide/essentials/class-and-style.html#binding-html-classes and since the Svelte team has no current plans to add this feature, I've been using the following solution:

We create the useClasses.js file, I like to place it in my Helpers folder, but obviously you can save it anywhere you would like to.

export default function useClasses(obj) {
    let classes = [];

    Object.keys(obj).forEach((key) => {
        if (obj[key]) classes.push(key);

    return classes.join(" ");

We can use this function like this:

<div class="{useClasses({
    'bg-white text-black': conditionA && !darkMode,
    'bg-black text-white': conditionB && darkMode 

That's all there is to it.

If you have any questions, please leave a comment below.