Fixed Default Date values in nested objects

Author: ciscoheat

CHANGELOG.md

@@ -11,6 +11,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 - Zod 4 adapter: Allow top-level `.transform()` and `.refine()` in schemas. [#646](https://github.com/ciscoheat/sveltekit-superforms/issues/646).
 - Zod 4 adapter: Now respects global `customError` configuration when no explicit error map is provided. The adapter prioritizes `customError` over `localeError`. [#618](https://github.com/ciscoheat/sveltekit-superforms/issues/618).
+- Zod 4 adapter: Fixed Default Date values in nested objects. [#650](https://github.com/ciscoheat/sveltekit-superforms/issues/650).
 
 ## [2.28.0] - 2025-10-19
 

src/lib/jsonSchema/schemaDefaults.ts

@@ -127,10 +127,47 @@ function _defaultValues(schema: JSONSchema, isOptional: boolean, path: string[])
 		for (const [key, objSchema] of Object.entries(info.properties)) {
 			assertSchema(objSchema, [...path, key]);
 
-			const def =
-				objectDefaults && objectDefaults[key] !== undefined
-					? objectDefaults[key]
-					: _defaultValues(objSchema, !info.required?.includes(key), [...path, key]);
+			// Determine the default value for this property. If an object-level default
+			// was provided, attempt to convert it to the correct typed form using the
+			// property's schema information (e.g. convert ISO strings back to Date).
+			let def;
+			if (objectDefaults && objectDefaults[key] !== undefined) {
+				try {
+					const propInfo = schemaInfo(objSchema, !info.required?.includes(key), [...path, key]);
+					if (propInfo) {
+						// Use the first resolved type to format simple values (dates, sets, maps, bigint, symbol)
+						const propType = propInfo.types[0];
+						// If property is an object and the provided default is an object,
+						// we need to recursively process it to convert nested values (e.g. Date strings to Dates)
+						if (
+							propType === 'object' &&
+							typeof objectDefaults[key] === 'object' &&
+							objectDefaults[key] !== null &&
+							!Array.isArray(objectDefaults[key])
+						) {
+							// Create a temporary schema with the parent's default to recursively process it
+							const schemaWithDefault: JSONSchema = {
+								...objSchema,
+								// eslint-disable-next-line @typescript-eslint/no-explicit-any
+								default: objectDefaults[key] as any
+							};
+							def = _defaultValues(schemaWithDefault, !info.required?.includes(key), [
+								...path,
+								key
+							]);
+						} else {
+							def = formatDefaultValue(propType, objectDefaults[key]);
+						}
+					} else {
+						def = objectDefaults[key];
+					}
+				} catch {
+					// If anything goes wrong determining/formatting, fall back to provided value
+					def = objectDefaults[key];
+				}
+			} else {
+				def = _defaultValues(objSchema, !info.required?.includes(key), [...path, key]);
+			}
 
 			//if (def !== undefined) output[key] = def;
 			if (output === undefined) output = {};

src/tests/issue-650.test.ts

@@ -0,0 +1,111 @@
+import { describe, it, expect } from 'vitest';
+import { superValidate } from '$lib/superValidate.js';
+import { zod } from '$lib/adapters/zod4.js';
+import { z } from 'zod/v4';
+
+describe('Issue 650 - Zod 4 Default Date values in nested objects', () => {
+	it('should handle default dates in nested objects correctly', async () => {
+		const schema = z.object({
+			name: z.string().min(2),
+			email: z.string().email(),
+			dateRange: z
+				.object({
+					start: z.date(),
+					end: z.date()
+				})
+				.default({
+					start: new Date('2025-10-29T10:47:03.068Z'),
+					end: new Date('2025-10-29T10:47:03.068Z')
+				}),
+			dateRangeIndividual: z.object({
+				start: z.date().default(new Date('2025-10-29T10:52:25.537Z')),
+				end: z.date().default(new Date('2025-10-29T10:52:25.537Z'))
+			}),
+			date: z.date().default(new Date('2025-10-29T10:47:03.068Z'))
+		});
+
+		const form = await superValidate(zod(schema));
+		const data = form.data as any; // eslint-disable-line @typescript-eslint/no-explicit-any
+
+		// All dates should be Date objects, not strings
+		expect(data.dateRange.start).toBeInstanceOf(Date);
+		expect(data.dateRange.end).toBeInstanceOf(Date);
+		expect(data.dateRangeIndividual.start).toBeInstanceOf(Date);
+		expect(data.dateRangeIndividual.end).toBeInstanceOf(Date);
+		expect(data.date).toBeInstanceOf(Date);
+
+		// Verify the actual date values match what was set
+		expect(data.dateRange.start.toISOString()).toBe('2025-10-29T10:47:03.068Z');
+		expect(data.dateRange.end.toISOString()).toBe('2025-10-29T10:47:03.068Z');
+		expect(data.dateRangeIndividual.start.toISOString()).toBe('2025-10-29T10:52:25.537Z');
+		expect(data.dateRangeIndividual.end.toISOString()).toBe('2025-10-29T10:52:25.537Z');
+		expect(data.date.toISOString()).toBe('2025-10-29T10:47:03.068Z');
+	});
+
+	it('should handle nested objects with default dates at multiple levels', async () => {
+		const schema = z.object({
+			level1: z
+				.object({
+					level2: z
+						.object({
+							date: z.date()
+						})
+						.default({
+							date: new Date('2025-01-01T00:00:00.000Z')
+						})
+				})
+				.default({
+					level2: {
+						date: new Date('2025-01-01T00:00:00.000Z')
+					}
+				})
+		});
+
+		const form = await superValidate(zod(schema));
+		const data = form.data as any; // eslint-disable-line @typescript-eslint/no-explicit-any
+
+		expect(data.level1.level2.date).toBeInstanceOf(Date);
+		expect(data.level1.level2.date.toISOString()).toBe('2025-01-01T00:00:00.000Z');
+	});
+
+	it('should handle mixed default values in nested objects', async () => {
+		const schema = z.object({
+			settings: z
+				.object({
+					theme: z.string(),
+					createdAt: z.date(),
+					count: z.number()
+				})
+				.default({
+					theme: 'dark',
+					createdAt: new Date('2025-10-29T00:00:00.000Z'),
+					count: 42
+				})
+		});
+
+		const form = await superValidate(zod(schema));
+		const data = form.data as any; // eslint-disable-line @typescript-eslint/no-explicit-any
+
+		expect(data.settings.theme).toBe('dark');
+		expect(data.settings.createdAt).toBeInstanceOf(Date);
+		expect(data.settings.createdAt.toISOString()).toBe('2025-10-29T00:00:00.000Z');
+		expect(data.settings.count).toBe(42);
+	});
+
+	it('should preserve individual field defaults when object has no default', async () => {
+		const schema = z.object({
+			timestamps: z.object({
+				created: z.date().default(new Date('2025-01-01T00:00:00.000Z')),
+				updated: z.date().default(new Date('2025-01-02T00:00:00.000Z'))
+			})
+		});
+
+		const form = await superValidate(zod(schema));
+		const data = form.data as any; // eslint-disable-line @typescript-eslint/no-explicit-any
+
+		expect(data.timestamps.created).toBeInstanceOf(Date);
+		expect(data.timestamps.updated).toBeInstanceOf(Date);
+		expect(data.timestamps.created.toISOString()).toBe('2025-01-01T00:00:00.000Z');
+		expect(data.timestamps.updated.toISOString()).toBe('2025-01-02T00:00:00.000Z');
+	});
+});