Add class to props.class

[Vulcagon]

<script lang="ts">
    import ChildComponent from './ChildComponent.svelte';
    import type { ComponentProps } from 'svelte';

    const { ...props }: ComponentProps<typeof ChildComponent> = $props();
</script>

<ChildComponent {...props} />

When having something like the above, how do I add a class to ChildComponent?

Since props.class can be a string, list or object you can't easily add a class to props.class.
Doing <ChildComponent class="new-class" {...props} /> doesn't work since props.class overrides class="new-class".
The syntax class:new-class={true} isn't allowed on Svelte components.

[brunnerh]

Objects and arrays are flattened by clsx, so if the component uses the class prop "correctly", you should be able to do:

<ChildComponent {...props} class={['new-class', props.class]} />

(You can also split off the class if you want to switch the order.)