fix(core): Preserve Date values passed to the expression isolate (#33322)

Co-authored-by: Claude Opus 4.8 (1M context) <[email protected]>

packages/@n8n/expression-runtime/src/__tests__/integration.test.ts

@@ -284,6 +284,34 @@ describe('Integration: ExpressionEvaluator + IsolatedVmBridge', () => {
 		});
 	});
 
+	describe('Date marshaling from workflow data', () => {
+		it('should read a top-level Date in $json as a Date, not {}', () => {
+			const data = { $json: { d: new Date('2026-06-30T20:34:04.498Z') } };
+
+			const result = evaluator.evaluate('{{ $json.d }}', data, caller);
+
+			expect(result).not.toEqual({});
+			expect(result).toBeInstanceOf(Date);
+			expect((result as Date).toISOString()).toBe('2026-06-30T20:34:04.498Z');
+		});
+
+		it('should read a nested Date in $json (e.g. Data Table createdAt)', () => {
+			const data = { $json: { row: { createdAt: new Date('2026-06-30T20:34:04.498Z') } } };
+
+			const result = evaluator.evaluate('{{ $json.row.createdAt }}', data, caller);
+
+			expect(result).toBeInstanceOf(Date);
+		});
+
+		it('should read a Date array element in $json', () => {
+			const data = { $json: { dates: [new Date('2026-06-30T20:34:04.498Z')] } };
+
+			const result = evaluator.evaluate('{{ $json.dates[0] }}', data, caller);
+
+			expect(result).toBeInstanceOf(Date);
+		});
+	});
+
 	it('should throw on invalid timezone', async () => {
 		const data = { $json: { x: 1 } };
 

packages/@n8n/expression-runtime/src/bridge/isolated-vm-bridge.ts

@@ -338,6 +338,12 @@ export class IsolatedVmBridge implements RuntimeBridge {
 					};
 				}
 
+				// Dates have no enumerable own keys; pass through instead of
+				// marshaling as an empty object.
+				if (value instanceof Date) {
+					return value;
+				}
+
 				// Handle objects - return metadata with keys
 				if (value !== null && typeof value === 'object') {
 					return {
@@ -396,6 +402,12 @@ export class IsolatedVmBridge implements RuntimeBridge {
 
 				const element = arr[index];
 
+				// Dates have no enumerable own keys; pass through instead of
+				// marshaling as an empty object.
+				if (element instanceof Date) {
+					return element;
+				}
+
 				// If element is object/array, return metadata
 				if (element !== null && typeof element === 'object') {
 					if (Array.isArray(element)) {