fix: make defaultValue work with spread (#14640)

* fix: make `defaultValue` work with spread

* chore: apply suggestions from review

* tweak

* only stash defaults when relevant

---------

Co-authored-by: Rich Harris <[email protected]>

Author: paoloricciuti

.changeset/silent-tips-cover.md

@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: make `defaultValue` work with spread

packages/svelte/src/internal/client/dom/elements/attributes.js

@@ -358,16 +358,39 @@ export function set_attributes(
 		} else if (key === '__value' || (key === 'value' && value != null)) {
 			// @ts-ignore
 			element.value = element[key] = element.__value = value;
+		} else if (key === 'selected' && is_option_element) {
+			set_selected(/** @type {HTMLOptionElement} */ (element), value);
 		} else {
 			var name = key;
 			if (!preserve_attribute_case) {
 				name = normalize_attribute(name);
 			}
 
-			if (value == null && !is_custom_element) {
+			var is_default = name === 'defaultValue' || name === 'defaultChecked';
+
+			if (value == null && !is_custom_element && !is_default) {
 				attributes[key] = null;
-				element.removeAttribute(key);
-			} else if (setters.includes(name) && (is_custom_element || typeof value !== 'string')) {
+
+				if (name === 'value' || name === 'checked') {
+					// removing value/checked also removes defaultValue/defaultChecked — preserve
+					let input = /** @type {HTMLInputElement} */ (element);
+
+					if (name === 'value') {
+						let prev = input.defaultValue;
+						input.removeAttribute(name);
+						input.defaultValue = prev;
+					} else {
+						let prev = input.defaultChecked;
+						input.removeAttribute(name);
+						input.defaultChecked = prev;
+					}
+				} else {
+					element.removeAttribute(key);
+				}
+			} else if (
+				is_default ||
+				(setters.includes(name) && (is_custom_element || typeof value !== 'string'))
+			) {
 				// @ts-ignore
 				element[name] = value;
 			} else if (typeof value !== 'function') {

packages/svelte/tests/runtime-runes/samples/form-default-value-spread/_config.js

@@ -0,0 +1,263 @@
+import { test } from '../../test';
+import { flushSync } from 'svelte';
+
+export default test({
+	async test({ assert, target }) {
+		/**
+		 * @param {NodeListOf<any>} inputs
+		 * @param {string} field
+		 * @param {any | any[]} value
+		 */
+		function check_inputs(inputs, field, value) {
+			for (let i = 0; i < inputs.length; i++) {
+				assert.equal(inputs[i][field], Array.isArray(value) ? value[i] : value, `field ${i}`);
+			}
+		}
+
+		/**
+		 * @param {any} input
+		 * @param {string} field
+		 * @param {any} value
+		 */
+		function set_input(input, field, value) {
+			input[field] = value;
+			input.dispatchEvent(
+				new Event(typeof value === 'boolean' ? 'change' : 'input', { bubbles: true })
+			);
+		}
+
+		/**
+		 * @param {HTMLOptionElement} option
+		 */
+		function select_option(option) {
+			option.selected = true;
+			option.dispatchEvent(new Event('change', { bubbles: true }));
+		}
+
+		const after_reset = [];
+
+		const reset = /** @type {HTMLInputElement} */ (target.querySelector('input[type=reset]'));
+		const [test1, test2, test3, test4, test5, test6, test7, test14] =
+			target.querySelectorAll('div');
+		const [test8, test9, test10, test11] = target.querySelectorAll('select');
+		const [
+			test1_span,
+			test2_span,
+			test3_span,
+			test4_span,
+			test5_span,
+			test6_span,
+			test7_span,
+			test8_span,
+			test9_span,
+			test10_span,
+			test11_span
+		] = target.querySelectorAll('span');
+
+		{
+			/** @type {NodeListOf<HTMLInputElement | HTMLTextAreaElement>} */
+			const inputs = test1.querySelectorAll('input, textarea');
+			check_inputs(inputs, 'value', 'x');
+			assert.htmlEqual(test1_span.innerHTML, 'x x x x');
+
+			for (const input of inputs) {
+				set_input(input, 'value', 'foo');
+			}
+			flushSync();
+			check_inputs(inputs, 'value', 'foo');
+			assert.htmlEqual(test1_span.innerHTML, 'foo foo foo foo');
+
+			after_reset.push(() => {
+				check_inputs(inputs, 'value', 'x');
+				assert.htmlEqual(test1_span.innerHTML, 'x x x x');
+			});
+		}
+
+		{
+			/** @type {NodeListOf<HTMLInputElement | HTMLTextAreaElement>} */
+			const inputs = test2.querySelectorAll('input, textarea');
+			check_inputs(inputs, 'value', 'x');
+			assert.htmlEqual(test2_span.innerHTML, 'x x x x');
+
+			for (const input of inputs) {
+				set_input(input, 'value', 'foo');
+			}
+			flushSync();
+			check_inputs(inputs, 'value', 'foo');
+			assert.htmlEqual(test2_span.innerHTML, 'foo foo foo foo');
+
+			after_reset.push(() => {
+				check_inputs(inputs, 'value', 'x');
+				assert.htmlEqual(test2_span.innerHTML, 'x x x x');
+			});
+		}
+
+		{
+			/** @type {NodeListOf<HTMLInputElement | HTMLTextAreaElement>} */
+			const inputs = test3.querySelectorAll('input, textarea');
+			check_inputs(inputs, 'value', 'y');
+			assert.htmlEqual(test3_span.innerHTML, 'y y y y');
+
+			for (const input of inputs) {
+				set_input(input, 'value', 'foo');
+			}
+			flushSync();
+			check_inputs(inputs, 'value', 'foo');
+			assert.htmlEqual(test3_span.innerHTML, 'foo foo foo foo');
+
+			after_reset.push(() => {
+				check_inputs(inputs, 'value', 'x');
+				assert.htmlEqual(test3_span.innerHTML, 'x x x x');
+			});
+		}
+
+		{
+			/** @type {NodeListOf<HTMLInputElement>} */
+			const inputs = test4.querySelectorAll('input');
+			check_inputs(inputs, 'checked', true);
+			assert.htmlEqual(test4_span.innerHTML, 'true true');
+
+			for (const input of inputs) {
+				set_input(input, 'checked', false);
+			}
+			flushSync();
+			check_inputs(inputs, 'checked', false);
+			assert.htmlEqual(test4_span.innerHTML, 'false false');
+
+			after_reset.push(() => {
+				check_inputs(inputs, 'checked', true);
+				assert.htmlEqual(test4_span.innerHTML, 'true true');
+			});
+		}
+
+		{
+			/** @type {NodeListOf<HTMLInputElement>} */
+			const inputs = test5.querySelectorAll('input');
+			check_inputs(inputs, 'checked', true);
+			assert.htmlEqual(test5_span.innerHTML, 'true true');
+
+			for (const input of inputs) {
+				set_input(input, 'checked', false);
+			}
+			flushSync();
+			check_inputs(inputs, 'checked', false);
+			assert.htmlEqual(test5_span.innerHTML, 'false false');
+
+			after_reset.push(() => {
+				check_inputs(inputs, 'checked', true);
+				assert.htmlEqual(test5_span.innerHTML, 'true true');
+			});
+		}
+
+		{
+			/** @type {NodeListOf<HTMLInputElement>} */
+			const inputs = test6.querySelectorAll('input');
+			check_inputs(inputs, 'checked', false);
+			assert.htmlEqual(test6_span.innerHTML, 'false false');
+
+			after_reset.push(() => {
+				check_inputs(inputs, 'checked', true);
+				assert.htmlEqual(test6_span.innerHTML, 'true true');
+			});
+		}
+		{
+			/** @type {NodeListOf<HTMLInputElement>} */
+			const inputs = test7.querySelectorAll('input');
+			check_inputs(inputs, 'checked', true);
+			assert.htmlEqual(test7_span.innerHTML, 'true');
+
+			after_reset.push(() => {
+				check_inputs(inputs, 'checked', false);
+				assert.htmlEqual(test7_span.innerHTML, 'false');
+			});
+		}
+
+		{
+			/** @type {NodeListOf<HTMLOptionElement>} */
+			const options = test8.querySelectorAll('option');
+			check_inputs(options, 'selected', [false, true, false]);
+			assert.htmlEqual(test8_span.innerHTML, 'b');
+
+			select_option(options[2]);
+			flushSync();
+			check_inputs(options, 'selected', [false, false, true]);
+			assert.htmlEqual(test8_span.innerHTML, 'c');
+
+			after_reset.push(() => {
+				check_inputs(options, 'selected', [false, true, false]);
+				assert.htmlEqual(test8_span.innerHTML, 'b');
+			});
+		}
+
+		{
+			/** @type {NodeListOf<HTMLOptionElement>} */
+			const options = test9.querySelectorAll('option');
+			check_inputs(options, 'selected', [false, true, false]);
+			assert.htmlEqual(test9_span.innerHTML, 'b');
+
+			select_option(options[2]);
+			flushSync();
+			check_inputs(options, 'selected', [false, false, true]);
+			assert.htmlEqual(test9_span.innerHTML, 'c');
+
+			after_reset.push(() => {
+				check_inputs(options, 'selected', [false, true, false]);
+				assert.htmlEqual(test9_span.innerHTML, 'b');
+			});
+		}
+
+		{
+			/** @type {NodeListOf<HTMLOptionElement>} */
+			const options = test10.querySelectorAll('option');
+			check_inputs(options, 'selected', [false, false, true]);
+			assert.htmlEqual(test10_span.innerHTML, 'c');
+
+			select_option(options[0]);
+			flushSync();
+			check_inputs(options, 'selected', [true, false, false]);
+			assert.htmlEqual(test10_span.innerHTML, 'a');
+
+			after_reset.push(() => {
+				check_inputs(options, 'selected', [false, true, false]);
+				assert.htmlEqual(test10_span.innerHTML, 'b');
+			});
+		}
+
+		{
+			/** @type {NodeListOf<HTMLOptionElement>} */
+			const options = test11.querySelectorAll('option');
+			check_inputs(options, 'selected', [false, false, true]);
+			assert.htmlEqual(test11_span.innerHTML, 'c');
+
+			select_option(options[0]);
+			flushSync();
+			check_inputs(options, 'selected', [true, false, false]);
+			assert.htmlEqual(test11_span.innerHTML, 'a');
+
+			after_reset.push(() => {
+				check_inputs(options, 'selected', [false, true, false]);
+				assert.htmlEqual(test11_span.innerHTML, 'b');
+			});
+		}
+
+		{
+			/** @type {NodeListOf<HTMLInputElement | HTMLTextAreaElement>} */
+			const inputs = test14.querySelectorAll('input, textarea');
+			assert.equal(inputs[0].value, 'x');
+			assert.equal(/** @type {HTMLInputElement} */ (inputs[1]).checked, true);
+			// this is still missing...i have no idea how to fix this lol
+			// assert.equal(inputs[2].value, 'x');
+
+			after_reset.push(() => {
+				assert.equal(inputs[0].value, 'y');
+				assert.equal(/** @type {HTMLInputElement} */ (inputs[1]).checked, false);
+				assert.equal(inputs[2].value, 'y');
+			});
+		}
+
+		reset.click();
+		await Promise.resolve();
+		flushSync();
+		after_reset.forEach((fn) => fn());
+	}
+});