From 4512462b6622406d03695f298efa603f4da04250 Mon Sep 17 00:00:00 2001
From: Dominic Gannaway <trueadm@users.noreply.github.com>
Date: Sat, 17 Aug 2024 14:32:49 +0100
Subject: [PATCH] chore: tweak each block logic (#12884)

* chore: tweak each block logic to avoid Array.from

* more tweaks

* lint

* Update packages/svelte/src/internal/client/dom/blocks/each.js

Co-authored-by: Rich Harris <rich.harris@vercel.com>

* Update packages/svelte/src/internal/client/dom/blocks/each.js

Co-authored-by: Rich Harris <rich.harris@vercel.com>

* Update packages/svelte/src/internal/client/dom/blocks/each.js

Co-authored-by: Rich Harris <rich.harris@vercel.com>

---------

Co-authored-by: Rich Harris <rich.harris@vercel.com>
---
 .../src/internal/client/dom/blocks/each.js    | 58 ++++++++++---------
 1 file changed, 31 insertions(+), 27 deletions(-)

diff --git a/packages/svelte/src/internal/client/dom/blocks/each.js b/packages/svelte/src/internal/client/dom/blocks/each.js
index 18785f7114..5788154db2 100644
--- a/packages/svelte/src/internal/client/dom/blocks/each.js
+++ b/packages/svelte/src/internal/client/dom/blocks/each.js
@@ -32,8 +32,8 @@ import {
 	resume_effect
 } from '../../reactivity/effects.js';
 import { source, mutable_source, set } from '../../reactivity/sources.js';
-import { is_array, is_frozen } from '../../../shared/utils.js';
-import { INERT, STATE_SYMBOL } from '../../constants.js';
+import { array_from, is_array } from '../../../shared/utils.js';
+import { INERT } from '../../constants.js';
 import { queue_micro_task } from '../task.js';
 import { current_effect } from '../../runtime.js';
 
@@ -139,7 +139,7 @@ export function each(node, flags, get_collection, get_key, render_fn, fallback_f
 			? collection
 			: collection == null
 				? []
-				: Array.from(collection);
+				: array_from(collection);
 
 		var length = array.length;
 
@@ -242,14 +242,14 @@ function reconcile(array, state, anchor, render_fn, flags, get_key) {
 	var first = state.first;
 	var current = first;
 
-	/** @type {Set<EachItem>} */
-	var seen = new Set();
+	/** @type {undefined | Set<EachItem>} */
+	var seen;
 
 	/** @type {EachItem | null} */
 	var prev = null;
 
-	/** @type {Set<EachItem>} */
-	var to_animate = new Set();
+	/** @type {undefined | Set<EachItem>} */
+	var to_animate;
 
 	/** @type {EachItem[]} */
 	var matched = [];
@@ -277,7 +277,7 @@ function reconcile(array, state, anchor, render_fn, flags, get_key) {
 
 			if (item !== undefined) {
 				item.a?.measure();
-				to_animate.add(item);
+				(to_animate ??= new Set()).add(item);
 			}
 		}
 	}
@@ -319,12 +319,12 @@ function reconcile(array, state, anchor, render_fn, flags, get_key) {
 			resume_effect(item.e);
 			if (is_animated) {
 				item.a?.unfix();
-				to_animate.delete(item);
+				(to_animate ??= new Set()).delete(item);
 			}
 		}
 
 		if (item !== current) {
-			if (seen.has(item)) {
+			if (seen !== undefined && seen.has(item)) {
 				if (matched.length < stashed.length) {
 					// more efficient to move later items to the front
 					var start = stashed[0];
@@ -372,7 +372,7 @@ function reconcile(array, state, anchor, render_fn, flags, get_key) {
 			stashed = [];
 
 			while (current !== null && current.k !== key) {
-				seen.add(current);
+				(seen ??= new Set()).add(current);
 				stashed.push(current);
 				current = current.next;
 			}
@@ -389,32 +389,36 @@ function reconcile(array, state, anchor, render_fn, flags, get_key) {
 		current = item.next;
 	}
 
-	const to_destroy = Array.from(seen);
+	if (current !== null || seen !== undefined) {
+		var to_destroy = seen === undefined ? [] : array_from(seen);
 
-	while (current !== null) {
-		to_destroy.push(current);
-		current = current.next;
-	}
-	var destroy_length = to_destroy.length;
+		while (current !== null) {
+			to_destroy.push(current);
+			current = current.next;
+		}
 
-	if (destroy_length > 0) {
-		var controlled_anchor = (flags & EACH_IS_CONTROLLED) !== 0 && length === 0 ? anchor : null;
+		var destroy_length = to_destroy.length;
 
-		if (is_animated) {
-			for (i = 0; i < destroy_length; i += 1) {
-				to_destroy[i].a?.measure();
-			}
+		if (destroy_length > 0) {
+			var controlled_anchor = (flags & EACH_IS_CONTROLLED) !== 0 && length === 0 ? anchor : null;
 
-			for (i = 0; i < destroy_length; i += 1) {
-				to_destroy[i].a?.fix();
+			if (is_animated) {
+				for (i = 0; i < destroy_length; i += 1) {
+					to_destroy[i].a?.measure();
+				}
+
+				for (i = 0; i < destroy_length; i += 1) {
+					to_destroy[i].a?.fix();
+				}
 			}
-		}
 
-		pause_effects(state, to_destroy, controlled_anchor, items);
+			pause_effects(state, to_destroy, controlled_anchor, items);
+		}
 	}
 
 	if (is_animated) {
 		queue_micro_task(() => {
+			if (to_animate === undefined) return;
 			for (item of to_animate) {
 				item.a?.apply();
 			}