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fix: improve array mutation validation warnings #14729

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fix: improve array mutation validation warnings #14729

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5 changes: 5 additions & 0 deletions .changeset/honest-news-bathe.md
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Original file line number Diff line number Diff line change
@@ -0,0 +1,5 @@
---
'svelte': patch
---

fix: improve array mutation validation warnings
13 changes: 10 additions & 3 deletions packages/svelte/src/internal/client/dev/equality.js
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Original file line number Diff line number Diff line change
@@ -1,6 +1,13 @@
import * as w from '../warnings.js';
import { get_proxied_value } from '../proxy.js';

/**
* @param {any} v
*/
function is_object(v) {
return typeof v === 'object' && v !== null;
}

export function init_array_prototype_warnings() {
const array_prototype = Array.prototype;
// The REPL ends up here over and over, and this prevents it from adding more and more patches
Expand All @@ -16,7 +23,7 @@ export function init_array_prototype_warnings() {
array_prototype.indexOf = function (item, from_index) {
const index = indexOf.call(this, item, from_index);

if (index === -1) {
if (index === -1 && is_object(item)) {
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What I don't quite understand is why the proxied version would give a different result - is it not updated yet to the latest value?

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@trueadm trueadm Dec 16, 2024 •
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We don't modify the original object on mutations to the proxied object, so here the proxied version is [] and the original object is [1], so it triggers the warning because it first checks if the proxied array has it, then checks if the original array has it.

const test = indexOf.call(get_proxied_value(this), get_proxied_value(item), from_index);

if (test !== -1) {
Expand All @@ -32,7 +39,7 @@ export function init_array_prototype_warnings() {
// `arguments` inside so passing undefined is different from not passing anything
const index = lastIndexOf.call(this, item, from_index ?? this.length - 1);

if (index === -1) {
if (index === -1 && is_object(item)) {
// we need to specify this.length - 1 because it's probably using something like
// `arguments` inside so passing undefined is different from not passing anything
const test = lastIndexOf.call(
Expand All @@ -52,7 +59,7 @@ export function init_array_prototype_warnings() {
array_prototype.includes = function (item, from_index) {
const has = includes.call(this, item, from_index);

if (!has) {
if (!has && is_object(item)) {
const test = includes.call(get_proxied_value(this), get_proxied_value(item), from_index);

if (test) {
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