Transition

About this component

One of Svelte’s strengths is its great support for transitions and animations. You are welcome and even encouraged to use them with this library when possible. So why bother with the Transition component?

There are a few reasons you may choose to use Transition:

• You are converting code from Tailwind UI which uses a Transition component. It may be simpler to just be able to port that code directly instead of replacing it with a Svelte transition.

• You want to use CSS class-based transitions (perhaps via Tailwind CSS classes, perhaps not) instead of using Svelte’s transition engine. In that case this component can help, especially by helping coordinate multiple transitions (one of the main features of the component).

Since the way this component works is based on CSS classes, we’ll be using Tailwind CSS transition classes for the examples. However, you are free to use your own transition classes, as long as they are globally available.

Basic example

The Transition accepts a show prop that controls whether the children should be shown or hidden, and a set of lifecycle props (like enterFrom and leaveTo) that let you add CSS classes at specific phases of a transition.

<script>
  import { Transition } from "@rgossiaux/svelte-headlessui";
  let show = false;
</script>

<button on:click={() => (show = !show)}> Toggle </button>
<Transition
  {show}
  enter="transition-opacity duration-75"
  enterFrom="opacity-0"
  enterTo="opacity-100"
  leave="transition-opacity duration-150"
  leaveFrom="opacity-100"
  leaveTo="opacity-0"
>
  I will fade in and out
</Transition>

Showing and hiding content

Wrap the content that should be conditionally rendered in a Transition component, and use the show prop to control whether the content should be visible or hidden.

<script>
  import { Transition } from "@rgossiaux/svelte-headlessui";
  let show = false;
</script>

<button on:click={() => (show = !show)}> Toggle </button>
<Transition {show}>I will appear and disappear</Transition>

The Transition component will render a div by default, but you can use the as prop to render a different element instead if needed. Any other HTML attributes (like class or style) can be added directly to the Transition the same way they would be for regular HTML elements.

<script>
  import { Transition } from "@rgossiaux/svelte-headlessui";
  let show = false;
</script>

<button on:click={() => (show = !show)}> Toggle </button>
<Transition {show} as="a" href="/my-url" style="font-weight: 700;">
  I will appear and disappear
</Transition>

Animating transitions

By default, a Transition will enter and leave instantly, which is probably not what you’re looking for if you’re using this component.

To animate your enter/leave transitions, add classes that provide the styling for each phase of the transitions using these props:

• enter: Applied the entire time an element is entering. Usually you define your duration and what properties you want to transition here: transition-opacity duration-75, for example.

• enterFrom: The starting point to enter from, like opacity-0 if something should fade in.

• enterTo: The ending point to enter to, like opacity-100 after fading in.

• leave: Applied the entire time an element is leaving. Usually you define your duration and what properties you want to transition here: transition-opacity duration-75, for example.

• leaveFrom: The starting point to leave from, like opacity-100 if something should fade out.

• leaveTo: The ending point to leave to, like opacity-0 after fading out.

Here’s an example:

<script>
  import { Transition } from "@rgossiaux/svelte-headlessui";
  let show = false;
</script>

<button on:click={() => (show = !show)}> Toggle </button>
<Transition
  {show}
  enter="transition-opacity duration-75"
  enterFrom="opacity-0"
  enterTo="opacity-100"
  leave="transition-opacity duration-150"
  leaveFrom="opacity-100"
  leaveTo="opacity-0"
>
  I will fade in and out
</Transition>

In this example, the transitioning element will take 75ms to enter (that’s the duration-75 class), and will transition the opacity property during that time (that’s transition-opacity).

It will start completely transparent before entering (that’s opacity-0 in the enterFrom phase), and fade in to completely opaque (opacity-100) when finished (that’s the enterTo phase).

When the element is being removed (the leave phase), it will transition the opacity property, and spend 150ms doing it (transition-opacity duration-150).

It will start as completely opaque (the opacity-100 in the leaveFrom phase), and finish as completely transparent (the opacity-0 in the leaveTo phase).

All of these props are optional, and will default to just an empty string.

Coordinating multiple transitions

Sometimes you need to transition multiple elements with different animations but all based on the same state. For example, say the user clicks a button to open a sidebar that slides over the screen, and you also need to fade-in a background overlay at the same time.

You can do this by wrapping the related elements with a parent Transition component, and wrapping each child that needs its own transition styles with a TransitionChild component, which will automatically communicate with the parent Transition and inherit the parent’s show state.

<script>
  import { Transition, TransitionChild } from "@rgossiaux/svelte-headlessui";
  export let show = false;
</script>

<!-- This `show` prop controls all nested `TransitionChild` components -->
<Transition {show}>
  <!-- Background overlay -->
  <TransitionChild
    enter="transition-opacity ease-linear duration-300"
    enterFrom="opacity-0"
    enterTo="opacity-100"
    leave="transition-opacity ease-linear duration-300"
    leaveFrom="opacity-100"
    leaveTo="opacity-0"
  >
    <!-- ... -->
  </TransitionChild>

  <!-- Sliding sidebar -->
  <TransitionChild
    enter="transition ease-in-out duration-300 transform"
    enterFrom="-translate-x-full"
    enterTo="translate-x-0"
    leave="transition ease-in-out duration-300 transform"
    leaveFrom="translate-x-0"
    leaveTo="-translate-x-full"
  >
    <!-- ... -->
  </TransitionChild>
</Transition>

The TransitionChild component has the exact same API as the Transition component, but with no show prop, since the show value is controlled by the parent.

Parent Transition components will always automatically wait for all children to finish transitioning before unmounting, so you don’t need to manage any of that timing yourself.

Transitioning on initial mount

If you want an element to transition the very first time it’s rendered, set the appear prop to true.

This is useful if you want something to transition in on initial page load, or when its parent is conditionally rendered.

<script>
  import { Transition, TransitionChild } from "@rgossiaux/svelte-headlessui";
  export let show = false;
</script>

<Transition
  {show}
  appear={true}
  enter="transition-opacity duration-75"
  enterFrom="opacity-0"
  enterTo="opacity-100"
  leave="transition-opacity duration-150"
  leaveFrom="opacity-100"
  leaveTo="opacity-0"
>
  <!-- Your content goes here -->
</Transition>

Component API

Transition

This component is also exported as TransitionRoot, to maintain compatibility with some Tailwind UI snippets.

This component also dispatches the following custom events, which are listened to using the Svelte on: directive:

These event names have been changed to match the names that Svelte uses for transitions, starting in version 2.0 of this library.

TransitionChild

This component also dispatches the following custom events, which are listened to using the Svelte on: directive: