folder.svelte

<script>
export let value = [1, [2, [3]]];
function extend(idx) {
	return () => {
		view[idx] = value[idx];
	};
}
function strip(idx) {
	return () => {
		console.log('strip', view[idx]);
		view[idx] = extend(idx);
		view = view;
		value = value;
		console.log('strip', view[idx]);
	};
}
let view = value.map((x, idx) => x instanceof Array ? extend(idx) : x);
</script>
<content>
{#each view as item, idx}
	{#if item.call}
	<i on:click={item}>folder</i>
	{:else if item.slice}
	<i on:click={strip(idx)}>+</i>
	<svelte:self value={item}></svelte:self> 
	{:else}
	<p>
	{item}
	</p>
	{/if}
{/each}
</content>
<style>
	p{user-select: none;}
	i{cursor: pointer; user-select: none; display: block;}
	content{padding-left: 3em;display:inline-block;}
</style>

https://svelte.dev/repl/91dbfc7f9eec4c37971c6981a374d955?version=3.46.4