Restart or re-init component in Svelte

Question

Is there an easy way to force a restart of Svelte components in place?

Restart use cases:

• Clear file list of HTML files input (you cannot reset the path / value)
• Nav bar dropdown collapse after item selection when using CSS hover

Maybe there are other solutions besides the restart, but lets use a component restart here.

Below the restart code which works fine for the upload use case:

SomeApp.svelte

<script>
      ...
      import Upload from "./upload/Upload.svelte";

      export let uid;  // firebase uid from auth

      // restart the Upload component after the upload 
      // to clear the filename of the <input type="file" ..../>  
      // restart by making use of a dynamic (falsy) component
      let upload_component = Upload;
      let restart = false;

      $: if (restart) {
         // use a falsy to stop / destroy this component 
         upload_component = null;
         // use a timer to queue a restart after the component has stopped
         setTimeout(() => {
           console.log('Upload component restarts')
           upload_component = Upload
         }, 0);
         console.log('Upload component restart queued');
         restart = false;  
      };

      ...
</script>


<!-- dynamic upload to restart the component when finished-->
<svelte:component uid={uid} this={upload_component} bind:finished={restart}/>

Upload.svelte

<script>
    import { onDestroy } from 'svelte';
    import { uploadCsv } from './upload.js'

    export let uid = null;
    export let finished;

    function uploadCsvCallback(result) {
      console.log(result);
      finished = true;
    };

    onDestroy(() => {
      console.log('Upload component destroyed');
    });
</script>

<style>
     .float-right {
          float: right;
      }
</style>

<!-- Select a CSV file to batch import a Firestore collection -->
<input
    type="file" name="files" class="float-right" accept=".csv" 
    on:change={uploadCsv(uid, uploadCsvCallback)}
/>

Update:
A component gets destroyed if the components is not rendered. So you can stop and restart a component when you toggle an if block arround a component.

Example:
1. toggle run from true to false to destroy the Upload component
2. and toggle run from false to true to restart the Upload component

{#if run}
  <Upload .....>
{/if}

And you can use a timer to toggle the restart.

run = true:
function restartComponent() {
  restart = false;  // stop / destroy
  setTimeout(() => run = true, 0); // and queue a restart
}

Answer 1

Yes, using a {#key} block:

<script>
import YourComponent from "./YourComponent.svelte"

let unique = {}

function restart() {
  unique = {} // every {} is unique, {} === {} evaluates to false
}
</script>

{#key unique}
  <YourComponent />
{/key}

<button on:click={restart}>Restart</button>

REPL

{#key} was introduced in Svelte v3.28, before that you needed to use a keyed {#each} block with only one item