Keep alive Svelte action

action.js

const instances = {};

export default function (node, {id, componentClass}) {
  if (instances[id]) {
    node.appendChild(instances[id]);
  } else {
    const wrapper = document.createElement('div');

    const instance = new componentClass({
      target: wrapper
    });

    instances[id] = wrapper;

    node.appendChild(wrapper);
  }
}

Example.svelte

<script>
  import keepAlive from "./action.js";
  import Component from './Component.svelte';
</script>

<div use:keepAlive={{id: 'some-manual-id', componentClass: Component}}/>

A sample solution for Svelte 5.