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 <rich.harris@vercel.com>

.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;
+
+				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 (setters.includes(name) && (is_custom_element || typeof value !== 'string')) {
+				}
+			} 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());
+	}
+});

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

@@ -0,0 +1,199 @@
+<script>
+	let spread = {};
+
+	let value1 = $state();
+	let value2 = $state();
+	let value3 = $state();
+	let value4 = $state();
+	let value5 = $state();
+	let value6 = $state();
+	let value7 = $state();
+	let value8 = $state();
+	let value9 = $state(null);
+	let value10 = $state(null);
+	let value11 = $state(null);
+	let value12 = $state(null);
+	let value13 = $state(null);
+	let value14 = $state(null);
+	let value15 = $state(null);
+	let value16 = $state(null);
+	let value17 = $state('y');
+	let value18 = $state('y');
+	let value19 = $state('y');
+	let value20 = $state('y');
+	let value21 = $state('y');
+	let value22 = $state('y');
+	let value23 = $state('y');
+	let value24 = $state('y');
+
+	let checked1 = $state();
+	let checked2 = $state();
+	let checked3 = $state();
+	let checked4 = $state();
+	let checked5 = $state(null);
+	let checked6 = $state(null);
+	let checked7 = $state(null);
+	let checked8 = $state(null);
+	let checked9 = $state(false);
+	let checked10 = $state(false);
+	let checked11 = $state(false);
+	let checked12 = $state(false);
+	let checked13 = $state(true);
+	let checked14 = $state(true);
+ 
+
+	let selected1 = $state();
+	let selected2 = $state();
+	let selected3 = $state('c');
+	let selected4 = $state('c');
+	let selected5 = $state(['c']);
+	let selected6 = $state(['c']);
+
+	let defaultValue = $state('x');
+	let defaultChecked = $state(true);
+</script>
+
+<form>
+	<p>Input/Textarea value</p>
+	<!-- defaultValue=x, value=undefined -->
+	<div class="test-1">
+		<input {defaultValue} bind:value={value1} {...spread} />
+		<input {defaultValue} value={value2} {...spread} />
+		<input defaultValue="x" bind:value={value3} {...spread} />
+		<input defaultValue="x" value={value4} {...spread} />
+		<textarea {defaultValue} value={value5} {...spread}></textarea>
+		<textarea {defaultValue} bind:value={value6} {...spread}></textarea>
+		<textarea defaultValue="x" value={value7} {...spread}></textarea>
+		<textarea defaultValue="x" bind:value={value8} {...spread}></textarea>
+	</div>
+
+	<!-- defaultValue=x, value=null -->
+	<div class="test-2">
+		<input {defaultValue} bind:value={value9} {...spread} />
+		<input {defaultValue} value={value10} {...spread} />
+		<input defaultValue="x" value={value11} {...spread} />
+		<input defaultValue="x" bind:value={value12} {...spread} />
+		<textarea {defaultValue} value={value13} {...spread}></textarea>
+		<textarea {defaultValue} bind:value={value14} {...spread}></textarea>
+		<textarea defaultValue="x" value={value15} {...spread}></textarea>
+		<textarea defaultValue="x" bind:value={value16} {...spread}></textarea>
+	</div>
+
+	<!-- defaultValue=x, value=y -->
+	<div class="test-3">
+		<input {defaultValue} bind:value={value17} {...spread} />
+		<input {defaultValue} value={value18} {...spread} />
+		<input defaultValue="x" value={value19} {...spread} />
+		<input defaultValue="x" bind:value={value20} {...spread} />
+		<textarea {defaultValue} value={value21} {...spread}></textarea>
+		<textarea {defaultValue} bind:value={value22} {...spread}></textarea>
+		<textarea defaultValue="x" value={value23} {...spread}></textarea>
+		<textarea defaultValue="x" bind:value={value24} {...spread}></textarea>
+	</div>
+
+	<p>Input checked</p>
+	<!-- defaultChecked=true, checked=undefined -->
+	<div class="test-4">
+		<input type="checkbox" {defaultChecked} checked={checked1} {...spread} />
+		<input type="checkbox" {defaultChecked} bind:checked={checked2} {...spread} />
+		<input type="checkbox" defaultChecked checked={checked3} {...spread} />
+		<input type="checkbox" defaultChecked bind:checked={checked4} {...spread} />
+	</div>
+
+	<!-- defaultChecked=true, checked=null -->
+	<div class="test-5">
+		<input type="checkbox" {defaultChecked} checked={checked5} {...spread} />
+		<input type="checkbox" {defaultChecked} bind:checked={checked6} {...spread} />
+		<input type="checkbox" defaultChecked checked={checked7} {...spread} />
+		<input type="checkbox" defaultChecked bind:checked={checked8} {...spread} />
+	</div>
+
+	<!-- defaultChecked=true, checked=false -->
+	<div class="test-6">
+		<input type="checkbox" {defaultChecked} checked={checked9} {...spread} />
+		<input type="checkbox" {defaultChecked} bind:checked={checked10} {...spread} />
+		<input type="checkbox" defaultChecked checked={checked11} {...spread} />
+		<input type="checkbox" defaultChecked bind:checked={checked12} {...spread} />
+	</div>
+
+	<!-- defaultChecked=false, checked=true -->
+	<div class="test-7">
+		<input type="checkbox" defaultChecked={false} checked={checked13} {...spread} />
+		<input type="checkbox" defaultChecked={false} bind:checked={checked14} {...spread} />
+	</div>
+
+	<!-- no support for bind:group; too complex + we may deprecate it in favor of bind:checked={get,set} -->
+
+	<p>Select (single)</p>
+	<!-- select with static checked, value=undefined-->
+	<select bind:value={selected1}>
+		<option value="a">A</option>
+		<option value="b" selected {...spread}>B</option>
+		<option value="c">C</option>
+	</select>
+
+	<!-- select with dynamic checked, value=undefined-->
+	<select bind:value={selected2}>
+		<option value="a">A</option>
+		<option value="b" selected={defaultChecked}>B</option>
+		<option value="c">C</option>
+	</select>
+
+	<!-- select with static checked, value=something else than default-->
+	<select bind:value={selected3}>
+		<option value="a">A</option>
+		<option value="b" selected {...spread}>B</option>
+		<option value="c">C</option>
+	</select>
+
+	<!-- select with dynamic checked, value=something else than default-->
+	<select bind:value={selected4}>
+		<option value="a">A</option>
+		<option value="b" selected={defaultChecked}>B</option>
+		<option value="c">C</option>
+	</select>
+
+	<p>Select (multiple)</p>
+    <!-- There's no possibility to have the selected attribute influence a multi select initially,
+	     because we require the value to be an array -->
+
+	<!-- select with static checked, value=something else than default-->
+	<select multiple bind:value={selected5}>
+		<option value="a">A</option>
+		<option value="b" selected {...spread}>B</option>
+		<option value="c">C</option>
+	</select>
+
+	<!-- select with dynamic checked, value=something else than default-->
+	<select multiple bind:value={selected6}>
+		<option value="a">A</option>
+		<option value="b" selected={defaultChecked}>B</option>
+		<option value="c">C</option>
+	</select>
+
+	<p>Static values</p>
+	<div class="test-14">
+		<input value="x" defaultValue="y" {...spread} />
+		<input type="checkbox" checked defaultChecked={false} {...spread} />
+		<textarea defaultValue="y" {...spread}>x</textarea>
+	</div>
+
+	<input type="reset" value="Reset" />
+</form>
+
+<p>
+	Bound values:
+	<span class="test-1">{value1} {value3} {value6} {value8}</span>
+	<span class="test-2">{value9} {value12} {value14} {value16}</span>
+	<span class="test-3">{value17} {value20} {value22} {value24}</span>
+	<span class="test-4">{checked2} {checked4}</span>
+	<span class="test-5">{checked6} {checked8}</span>
+	<span class="test-6">{checked10} {checked12}</span>
+	<span class="test-7">{checked14}</span>
+	<span class="test-8">{selected1}</span>
+	<span class="test-9">{selected2}</span>
+	<span class="test-10">{selected3}</span>
+	<span class="test-11">{selected4}</span>
+	<span class="test-12">{selected5}</span>
+	<span class="test-13">{selected6}</span>
+</p>

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

@@ -68,7 +68,6 @@ export default test({
 			assert.htmlEqual(test1_span.innerHTML, 'foo foo foo foo');
 
 			after_reset.push(() => {
-				console.log('-------------');
 				check_inputs(inputs, 'value', 'x');
 				assert.htmlEqual(test1_span.innerHTML, 'x x x x');
 			});
@@ -88,7 +87,6 @@ export default test({
 			assert.htmlEqual(test2_span.innerHTML, 'foo foo foo foo');
 
 			after_reset.push(() => {
-				console.log('-------------');
 				check_inputs(inputs, 'value', 'x');
 				assert.htmlEqual(test2_span.innerHTML, 'x x x x');
 			});