Slots are a handy way to let you define components that can be composed together.

And vice versa, depending on your point of view, slots are a handy way to configure a component you are importing.

Here’s how they work.

In a component you can define a slot using the <slot /> (or <slot></slot>) syntax.

Here’s a Button.svelte component that simply prints a <button> HTML tag:

<button><slot /></button>

For React developers, this is basically the same as <button>{props.children}</button>

Any component importing it can define content that is going to be put into the slot by adding it into the component’s opening and closing tags:

<script>
import Button from './Button.svelte'
</script>

<Button>Insert this into the slot</Button>

You can define a default, which is used if the slot is not filled:

<button>
<slot>
Default text for the button
</slot>
</button>

You can have more than one slot in a component, and you can distinguish one from the other using named slots. The single unnamed slot will be the default one:

<slot name="before" />
<button>
<slot />
</button>
<slot name="after" />

Here’s how you would use it:

<script>
import Button from './Button.svelte'
</script>

<Button>
Insert this into the slot
</Button>

And this would render the following to the DOM:

<p slot="before">Add this before</p>
<button>
Insert this into the slot
</button>
<p slot="after">Add this after</p>