fix: prevent duplicate dependencies without using array.includes (#17503)

* fix: prevent duplicate dependencies without using array.includes

* changeset

.changeset/gold-coats-change.md

@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: faster deduplication of dependencies

packages/svelte/src/internal/client/runtime.js

@@ -309,6 +309,20 @@ export function update_reaction(reaction) {
 		if (previous_reaction !== null && previous_reaction !== reaction) {
 			read_version++;
 
+			// update the `rv` of the previous reaction's deps — both existing and new —
+			// so that they are not added again
+			if (previous_reaction.deps !== null) {
+				for (let i = 0; i < previous_skipped_deps; i += 1) {
+					previous_reaction.deps[i].rv = read_version;
+				}
+			}
+
+			if (previous_deps !== null) {
+				for (const dep of previous_deps) {
+					dep.rv = read_version;
+				}
+			}
+
 			if (untracked_writes !== null) {
 				if (previous_untracked_writes === null) {
 					previous_untracked_writes = untracked_writes;
@@ -526,7 +540,7 @@ export function get(signal) {
 						skipped_deps++;
 					} else if (new_deps === null) {
 						new_deps = [signal];
-					} else if (!new_deps.includes(signal)) {
+					} else {
 						new_deps.push(signal);
 					}
 				}