feat: Add once for each item support for JS task runner (no-changelog) (#11109)

packages/@n8n/nodes-langchain/nodes/chains/InformationExtractor/InformationExtractor.node.ts

@@ -262,7 +262,7 @@ export class InformationExtractor implements INodeType {
 			}
 
 			const zodSchemaSandbox = getSandboxWithZod(this, jsonSchema, 0);
-			const zodSchema = (await zodSchemaSandbox.runCode()) as z.ZodSchema<object>;
+			const zodSchema = await zodSchemaSandbox.runCode<z.ZodSchema<object>>();
 
 			parser = OutputFixingParser.fromLLM(llm, StructuredOutputParser.fromZodSchema(zodSchema));
 		}

packages/@n8n/nodes-langchain/nodes/code/Code.node.ts

@@ -107,7 +107,7 @@ function getSandbox(
 	}
 	// eslint-disable-next-line @typescript-eslint/unbound-method
 
-	const sandbox = new JavaScriptSandbox(context, code, itemIndex, this.helpers, {
+	const sandbox = new JavaScriptSandbox(context, code, this.helpers, {
 		resolver: vmResolver,
 	});
 
@@ -368,7 +368,7 @@ export class Code implements INodeType {
 		}
 
 		const sandbox = getSandbox.call(this, code.supplyData.code, { itemIndex });
-		const response = (await sandbox.runCode()) as Tool;
+		const response = await sandbox.runCode<Tool>();
 
 		return {
 			response: logWrapper(response, this),

packages/@n8n/nodes-langchain/nodes/output_parser/OutputParserStructured/OutputParserStructured.node.ts

@@ -48,7 +48,7 @@ export class N8nStructuredOutputParser<T extends z.ZodTypeAny> extends Structure
 		sandboxedSchema: JavaScriptSandbox,
 		nodeVersion: number,
 	): Promise<StructuredOutputParser<z.ZodType<object, z.ZodTypeDef, object>>> {
-		const zodSchema = (await sandboxedSchema.runCode()) as z.ZodSchema<object>;
+		const zodSchema = await sandboxedSchema.runCode<z.ZodSchema<object>>();
 
 		let returnSchema: z.ZodSchema<object>;
 		if (nodeVersion === 1) {

packages/@n8n/nodes-langchain/nodes/tools/ToolCode/ToolCode.node.ts

@@ -199,9 +199,9 @@ export class ToolCode implements INodeType {
 
 			let sandbox: Sandbox;
 			if (language === 'javaScript') {
-				sandbox = new JavaScriptSandbox(context, code, index, this.helpers);
+				sandbox = new JavaScriptSandbox(context, code, this.helpers);
 			} else {
-				sandbox = new PythonSandbox(context, code, index, this.helpers);
+				sandbox = new PythonSandbox(context, code, this.helpers);
 			}
 
 			sandbox.on(
@@ -216,7 +216,7 @@ export class ToolCode implements INodeType {
 
 		const runFunction = async (query: string | IDataObject): Promise<string> => {
 			const sandbox = getSandbox(query, itemIndex);
-			return await (sandbox.runCode() as Promise<string>);
+			return await sandbox.runCode<string>();
 		};
 
 		const toolHandler = async (query: string | IDataObject): Promise<string> => {
@@ -274,7 +274,7 @@ export class ToolCode implements INodeType {
 						: jsonParse<JSONSchema7>(inputSchema);
 
 				const zodSchemaSandbox = getSandboxWithZod(this, jsonSchema, 0);
-				const zodSchema = (await zodSchemaSandbox.runCode()) as DynamicZodObject;
+				const zodSchema = await zodSchemaSandbox.runCode<DynamicZodObject>();
 
 				tool = new DynamicStructuredTool<typeof zodSchema>({
 					schema: zodSchema,

packages/@n8n/nodes-langchain/nodes/tools/ToolWorkflow/ToolWorkflow.node.ts

@@ -530,7 +530,7 @@ export class ToolWorkflow implements INodeType {
 						: jsonParse<JSONSchema7>(inputSchema);
 
 				const zodSchemaSandbox = getSandboxWithZod(this, jsonSchema, 0);
-				const zodSchema = (await zodSchemaSandbox.runCode()) as DynamicZodObject;
+				const zodSchema = await zodSchemaSandbox.runCode<DynamicZodObject>();
 
 				tool = new DynamicStructuredTool<typeof zodSchema>({
 					schema: zodSchema,

packages/@n8n/nodes-langchain/utils/schemaParsing.ts

@@ -57,7 +57,6 @@ export function getSandboxWithZod(ctx: IExecuteFunctions, schema: JSONSchema7, i
 			const itemSchema = new Function('z', 'return (' + zodSchema + ')')(z)
 			return itemSchema
 		`,
-		itemIndex,
 		ctx.helpers,
 		{ resolver: vmResolver },
 	);

packages/@n8n/task-runner/package.json

@@ -6,13 +6,14 @@
     "start": "node dist/start.js",
     "dev": "pnpm build && pnpm start",
     "typecheck": "tsc --noEmit",
-    "build": "tsc -p ./tsconfig.build.json",
+    "build": "tsc -p ./tsconfig.build.json && tsc-alias -p tsconfig.build.json",
     "format": "biome format --write src",
     "format:check": "biome ci src",
-    "test": "echo \"Error: no tests in this package\" && exit 0",
+    "test": "jest",
+    "test:watch": "jest --watch",
     "lint": "eslint . --quiet",
     "lintfix": "eslint . --fix",
-    "watch": "tsc -p tsconfig.build.json --watch"
+    "watch": "concurrently \"tsc -w -p tsconfig.build.json\" \"tsc-alias -w -p tsconfig.build.json\""
   },
   "main": "dist/start.js",
   "module": "src/start.ts",

packages/@n8n/task-runner/src/__tests__/code.test.ts

@@ -0,0 +1,319 @@
+import type { CodeExecutionMode, IDataObject, WorkflowExecuteMode } from 'n8n-workflow';
+
+import { JsTaskRunner, type AllCodeTaskData, type JSExecSettings } from '@/code';
+import type { Task } from '@/task-runner';
+import { ValidationError } from '@/validation-error';
+
+import { newAllCodeTaskData, newTaskWithSettings, withPairedItem, wrapIntoJson } from './test-data';
+
+jest.mock('ws');
+
+describe('JsTaskRunner', () => {
+	const jsTaskRunner = new JsTaskRunner('taskType', 'ws://localhost', 'grantToken', 1);
+
+	const execTaskWithParams = async ({
+		task,
+		taskData,
+	}: {
+		task: Task<JSExecSettings>;
+		taskData: AllCodeTaskData;
+	}) => {
+		jest.spyOn(jsTaskRunner, 'requestData').mockResolvedValue(taskData);
+		return await jsTaskRunner.executeTask(task);
+	};
+
+	afterEach(() => {
+		jest.restoreAllMocks();
+	});
+
+	describe('console', () => {
+		test.each<[CodeExecutionMode, WorkflowExecuteMode]>([
+			['runOnceForAllItems', 'cli'],
+			['runOnceForAllItems', 'error'],
+			['runOnceForAllItems', 'integrated'],
+			['runOnceForAllItems', 'internal'],
+			['runOnceForAllItems', 'retry'],
+			['runOnceForAllItems', 'trigger'],
+			['runOnceForAllItems', 'webhook'],
+			['runOnceForEachItem', 'cli'],
+			['runOnceForEachItem', 'error'],
+			['runOnceForEachItem', 'integrated'],
+			['runOnceForEachItem', 'internal'],
+			['runOnceForEachItem', 'retry'],
+			['runOnceForEachItem', 'trigger'],
+			['runOnceForEachItem', 'webhook'],
+		])(
+			'should make an rpc call for console log in %s mode when workflow mode is %s',
+			async (nodeMode, workflowMode) => {
+				jest.spyOn(console, 'log').mockImplementation(() => {});
+				jest.spyOn(jsTaskRunner, 'makeRpcCall').mockResolvedValue(undefined);
+				const task = newTaskWithSettings({
+					code: "console.log('Hello', 'world!'); return {}",
+					nodeMode,
+					workflowMode,
+				});
+
+				await execTaskWithParams({
+					task,
+					taskData: newAllCodeTaskData([wrapIntoJson({})]),
+				});
+
+				expect(console.log).toHaveBeenCalledWith('[JS Code]', 'Hello world!');
+				expect(jsTaskRunner.makeRpcCall).toHaveBeenCalledWith(task.taskId, 'logNodeOutput', [
+					'Hello world!',
+				]);
+			},
+		);
+
+		test.each<[CodeExecutionMode, WorkflowExecuteMode]>([
+			['runOnceForAllItems', 'manual'],
+			['runOnceForEachItem', 'manual'],
+		])(
+			"shouldn't make an rpc call for console log in %s mode when workflow mode is %s",
+			async (nodeMode, workflowMode) => {
+				jest.spyOn(jsTaskRunner, 'makeRpcCall').mockResolvedValue(undefined);
+				const task = newTaskWithSettings({
+					code: "console.log('Hello', 'world!'); return {}",
+					nodeMode,
+					workflowMode,
+				});
+
+				await execTaskWithParams({
+					task,
+					taskData: newAllCodeTaskData([wrapIntoJson({})]),
+				});
+
+				expect(jsTaskRunner.makeRpcCall).not.toHaveBeenCalled();
+			},
+		);
+	});
+
+	describe('runOnceForAllItems', () => {
+		const executeForAllItems = async ({
+			code,
+			inputItems,
+			settings,
+		}: { code: string; inputItems: IDataObject[]; settings?: Partial<JSExecSettings> }) => {
+			return await execTaskWithParams({
+				task: newTaskWithSettings({
+					code,
+					nodeMode: 'runOnceForAllItems',
+					...settings,
+				}),
+				taskData: newAllCodeTaskData(inputItems.map(wrapIntoJson)),
+			});
+		};
+
+		describe('continue on fail', () => {
+			it('should return an item with the error if continueOnFail is true', async () => {
+				const outcome = await executeForAllItems({
+					code: 'throw new Error("Error message")',
+					inputItems: [{ a: 1 }],
+					settings: { continueOnFail: true },
+				});
+
+				expect(outcome).toEqual({
+					result: [wrapIntoJson({ error: 'Error message' })],
+					customData: undefined,
+				});
+			});
+
+			it('should throw an error if continueOnFail is false', async () => {
+				await expect(
+					executeForAllItems({
+						code: 'throw new Error("Error message")',
+						inputItems: [{ a: 1 }],
+						settings: { continueOnFail: false },
+					}),
+				).rejects.toThrow('Error message');
+			});
+		});
+
+		describe('invalid output', () => {
+			test.each([['undefined'], ['42'], ['"a string"']])(
+				'should throw a ValidationError if the code output is %s',
+				async (output) => {
+					await expect(
+						executeForAllItems({
+							code: `return ${output}`,
+							inputItems: [{ a: 1 }],
+						}),
+					).rejects.toThrow(ValidationError);
+				},
+			);
+
+			it('should throw a ValidationError if some items are wrapped in json and some are not', async () => {
+				await expect(
+					executeForAllItems({
+						code: 'return [{b: 1}, {json: {b: 2}}]',
+						inputItems: [{ a: 1 }],
+					}),
+				).rejects.toThrow(ValidationError);
+			});
+		});
+
+		it('should return static items', async () => {
+			const outcome = await executeForAllItems({
+				code: 'return [{json: {b: 1}}]',
+				inputItems: [{ a: 1 }],
+			});
+
+			expect(outcome).toEqual({
+				result: [wrapIntoJson({ b: 1 })],
+				customData: undefined,
+			});
+		});
+
+		it('maps null into an empty array', async () => {
+			const outcome = await executeForAllItems({
+				code: 'return null',
+				inputItems: [{ a: 1 }],
+			});
+
+			expect(outcome).toEqual({
+				result: [],
+				customData: undefined,
+			});
+		});
+
+		it("should wrap items into json if they aren't", async () => {
+			const outcome = await executeForAllItems({
+				code: 'return [{b: 1}]',
+				inputItems: [{ a: 1 }],
+			});
+
+			expect(outcome).toEqual({
+				result: [wrapIntoJson({ b: 1 })],
+				customData: undefined,
+			});
+		});
+
+		it('should wrap single item into an array and json', async () => {
+			const outcome = await executeForAllItems({
+				code: 'return {b: 1}',
+				inputItems: [{ a: 1 }],
+			});
+
+			expect(outcome).toEqual({
+				result: [wrapIntoJson({ b: 1 })],
+				customData: undefined,
+			});
+		});
+
+		test.each([['items'], ['$input.all()'], ["$('Trigger').all()"]])(
+			'should have all input items in the context as %s',
+			async (expression) => {
+				const outcome = await executeForAllItems({
+					code: `return ${expression}`,
+					inputItems: [{ a: 1 }, { a: 2 }],
+				});
+
+				expect(outcome).toEqual({
+					result: [wrapIntoJson({ a: 1 }), wrapIntoJson({ a: 2 })],
+					customData: undefined,
+				});
+			},
+		);
+	});
+
+	describe('runForEachItem', () => {
+		const executeForEachItem = async ({
+			code,
+			inputItems,
+			settings,
+		}: { code: string; inputItems: IDataObject[]; settings?: Partial<JSExecSettings> }) => {
+			return await execTaskWithParams({
+				task: newTaskWithSettings({
+					code,
+					nodeMode: 'runOnceForEachItem',
+					...settings,
+				}),
+				taskData: newAllCodeTaskData(inputItems.map(wrapIntoJson)),
+			});
+		};
+
+		describe('continue on fail', () => {
+			it('should return an item with the error if continueOnFail is true', async () => {
+				const outcome = await executeForEachItem({
+					code: 'throw new Error("Error message")',
+					inputItems: [{ a: 1 }, { a: 2 }],
+					settings: { continueOnFail: true },
+				});
+
+				expect(outcome).toEqual({
+					result: [
+						withPairedItem(0, wrapIntoJson({ error: 'Error message' })),
+						withPairedItem(1, wrapIntoJson({ error: 'Error message' })),
+					],
+					customData: undefined,
+				});
+			});
+
+			it('should throw an error if continueOnFail is false', async () => {
+				await expect(
+					executeForEachItem({
+						code: 'throw new Error("Error message")',
+						inputItems: [{ a: 1 }],
+						settings: { continueOnFail: false },
+					}),
+				).rejects.toThrow('Error message');
+			});
+		});
+
+		describe('invalid output', () => {
+			test.each([['undefined'], ['42'], ['"a string"'], ['[]'], ['[1,2,3]']])(
+				'should throw a ValidationError if the code output is %s',
+				async (output) => {
+					await expect(
+						executeForEachItem({
+							code: `return ${output}`,
+							inputItems: [{ a: 1 }],
+						}),
+					).rejects.toThrow(ValidationError);
+				},
+			);
+		});
+
+		it('should return static items', async () => {
+			const outcome = await executeForEachItem({
+				code: 'return {json: {b: 1}}',
+				inputItems: [{ a: 1 }],
+			});
+
+			expect(outcome).toEqual({
+				result: [withPairedItem(0, wrapIntoJson({ b: 1 }))],
+				customData: undefined,
+			});
+		});
+
+		it('should filter out null values', async () => {
+			const outcome = await executeForEachItem({
+				code: 'return item.json.a === 1 ? item : null',
+				inputItems: [{ a: 1 }, { a: 2 }, { a: 3 }],
+			});
+
+			expect(outcome).toEqual({
+				result: [withPairedItem(0, wrapIntoJson({ a: 1 }))],
+				customData: undefined,
+			});
+		});
+
+		test.each([['item'], ['$input.item'], ['{ json: $json }']])(
+			'should have the current input item in the context as %s',
+			async (expression) => {
+				const outcome = await executeForEachItem({
+					code: `return ${expression}`,
+					inputItems: [{ a: 1 }, { a: 2 }],
+				});
+
+				expect(outcome).toEqual({
+					result: [
+						withPairedItem(0, wrapIntoJson({ a: 1 })),
+						withPairedItem(1, wrapIntoJson({ a: 2 })),
+					],
+					customData: undefined,
+				});
+			},
+		);
+	});
+});

packages/@n8n/task-runner/src/__tests__/test-data.ts

@@ -0,0 +1,148 @@
+import type { IDataObject, INode, INodeExecutionData, ITaskData } from 'n8n-workflow';
+import { NodeConnectionType } from 'n8n-workflow';
+import { nanoid } from 'nanoid';
+
+import type { AllCodeTaskData, JSExecSettings } from '@/code';
+import type { Task } from '@/task-runner';
+
+/**
+ * Creates a new task with the given settings
+ */
+export const newTaskWithSettings = (
+	settings: Partial<JSExecSettings> & Pick<JSExecSettings, 'code' | 'nodeMode'>,
+): Task<JSExecSettings> => ({
+	taskId: '1',
+	settings: {
+		workflowMode: 'manual',
+		continueOnFail: false,
+		mode: 'manual',
+		...settings,
+	},
+	active: true,
+	cancelled: false,
+});
+
+/**
+ * Creates a new node with the given options
+ */
+export const newNode = (opts: Partial<INode> = {}): INode => ({
+	id: nanoid(),
+	name: 'Test Node' + nanoid(),
+	parameters: {},
+	position: [0, 0],
+	type: 'n8n-nodes-base.code',
+	typeVersion: 1,
+	...opts,
+});
+
+/**
+ * Creates a new task data with the given options
+ */
+export const newTaskData = (opts: Partial<ITaskData> & Pick<ITaskData, 'source'>): ITaskData => ({
+	startTime: Date.now(),
+	executionTime: 0,
+	executionStatus: 'success',
+	...opts,
+});
+
+/**
+ * Creates a new all code task data with the given options
+ */
+export const newAllCodeTaskData = (
+	codeNodeInputData: INodeExecutionData[],
+	opts: Partial<AllCodeTaskData> = {},
+): AllCodeTaskData => {
+	const codeNode = newNode({
+		name: 'JsCode',
+		parameters: {
+			mode: 'runOnceForEachItem',
+			language: 'javaScript',
+			jsCode: 'return item',
+		},
+		type: 'n8n-nodes-base.code',
+		typeVersion: 2,
+	});
+	const manualTriggerNode = newNode({
+		name: 'Trigger',
+		type: 'n8n-nodes-base.manualTrigger',
+	});
+
+	return {
+		workflow: {
+			id: '1',
+			name: 'Test Workflow',
+			active: true,
+			connections: {
+				[manualTriggerNode.name]: {
+					main: [[{ node: codeNode.name, type: NodeConnectionType.Main, index: 0 }]],
+				},
+			},
+			nodes: [manualTriggerNode, codeNode],
+		},
+		inputData: {
+			main: [codeNodeInputData],
+		},
+		connectionInputData: codeNodeInputData,
+		node: codeNode,
+		runExecutionData: {
+			startData: {},
+			resultData: {
+				runData: {
+					[manualTriggerNode.name]: [
+						newTaskData({
+							source: [],
+							data: {
+								main: [codeNodeInputData],
+							},
+						}),
+					],
+				},
+				pinData: {},
+				lastNodeExecuted: manualTriggerNode.name,
+			},
+			executionData: {
+				contextData: {},
+				nodeExecutionStack: [],
+				metadata: {},
+				waitingExecution: {},
+				waitingExecutionSource: {},
+			},
+		},
+		runIndex: 0,
+		itemIndex: 0,
+		activeNodeName: codeNode.name,
+		contextNodeName: codeNode.name,
+		defaultReturnRunIndex: -1,
+		siblingParameters: {},
+		mode: 'manual',
+		selfData: {},
+		additionalData: {
+			formWaitingBaseUrl: '',
+			instanceBaseUrl: '',
+			restartExecutionId: '',
+			restApiUrl: '',
+			webhookBaseUrl: '',
+			webhookTestBaseUrl: '',
+			webhookWaitingBaseUrl: '',
+			variables: {},
+		},
+		...opts,
+	};
+};
+
+/**
+ * Wraps the given value into an INodeExecutionData object's json property
+ */
+export const wrapIntoJson = (json: IDataObject): INodeExecutionData => ({
+	json,
+});
+
+/**
+ * Adds the given index as the pairedItem property to the given INodeExecutionData object
+ */
+export const withPairedItem = (index: number, data: INodeExecutionData): INodeExecutionData => ({
+	...data,
+	pairedItem: {
+		item: index,
+	},
+});

packages/@n8n/task-runner/src/code.ts

@@ -1,28 +1,36 @@
 import { getAdditionalKeys } from 'n8n-core';
 import {
-	type INode,
-	type INodeType,
-	type ITaskDataConnections,
-	type IWorkflowExecuteAdditionalData,
 	WorkflowDataProxy,
-	type WorkflowParameters,
-	type IDataObject,
-	type IExecuteData,
-	type INodeExecutionData,
-	type INodeParameters,
-	type IRunExecutionData,
 	// type IWorkflowDataProxyAdditionalKeys,
 	Workflow,
-	type WorkflowExecuteMode,
+} from 'n8n-workflow';
+import type {
+	CodeExecutionMode,
+	INode,
+	INodeType,
+	ITaskDataConnections,
+	IWorkflowExecuteAdditionalData,
+	WorkflowParameters,
+	IDataObject,
+	IExecuteData,
+	INodeExecutionData,
+	INodeParameters,
+	IRunExecutionData,
+	WorkflowExecuteMode,
 } from 'n8n-workflow';
 import * as a from 'node:assert';
 import { runInNewContext, type Context } from 'node:vm';
 
+import { validateRunForAllItemsOutput, validateRunForEachItemOutput } from '@/result-validation';
+
 import type { TaskResultData } from './runner-types';
 import { type Task, TaskRunner } from './task-runner';
 
-interface JSExecSettings {
+export interface JSExecSettings {
 	code: string;
+	nodeMode: CodeExecutionMode;
+	workflowMode: WorkflowExecuteMode;
+	continueOnFail: boolean;
 
 	// For workflow data proxy
 	mode: WorkflowExecuteMode;
@@ -62,6 +70,12 @@ export interface AllCodeTaskData {
 	additionalData: PartialAdditionalData;
 }
 
+type CustomConsole = {
+	log: (...args: unknown[]) => void;
+};
+
+const noop = () => {};
+
 export class JsTaskRunner extends TaskRunner {
 	constructor(
 		taskType: string,
@@ -95,15 +109,154 @@ export class JsTaskRunner extends TaskRunner {
 			},
 		});
 
-		const dataProxy = new WorkflowDataProxy(
+		const customConsole = {
+			log:
+				settings.workflowMode === 'manual'
+					? noop
+					: (...args: unknown[]) => {
+							const logOutput = args
+								.map((arg) => (typeof arg === 'object' && arg !== null ? JSON.stringify(arg) : arg))
+								.join(' ');
+							console.log('[JS Code]', logOutput);
+							void this.makeRpcCall(task.taskId, 'logNodeOutput', [logOutput]);
+						},
+		};
+
+		const result =
+			settings.nodeMode === 'runOnceForAllItems'
+				? await this.runForAllItems(task.taskId, settings, allData, workflow, customConsole)
+				: await this.runForEachItem(task.taskId, settings, allData, workflow, customConsole);
+
+		return {
+			result,
+			customData: allData.runExecutionData.resultData.metadata,
+		};
+	}
+
+	/**
+	 * Executes the requested code for all items in a single run
+	 */
+	private async runForAllItems(
+		taskId: string,
+		settings: JSExecSettings,
+		allData: AllCodeTaskData,
+		workflow: Workflow,
+		customConsole: CustomConsole,
+	): Promise<INodeExecutionData[]> {
+		const dataProxy = this.createDataProxy(allData, workflow, allData.itemIndex);
+		const inputItems = allData.connectionInputData;
+
+		const context: Context = {
+			require,
+			module: {},
+			console: customConsole,
+
+			items: inputItems,
+			...dataProxy,
+			...this.buildRpcCallObject(taskId),
+		};
+
+		try {
+			const result = (await runInNewContext(
+				`module.exports = async function() {${settings.code}\n}()`,
+				context,
+			)) as TaskResultData['result'];
+
+			if (result === null) {
+				return [];
+			}
+
+			return validateRunForAllItemsOutput(result);
+		} catch (error) {
+			if (settings.continueOnFail) {
+				return [{ json: { error: this.getErrorMessageFromVmError(error) } }];
+			}
+
+			(error as Record<string, unknown>).node = allData.node;
+			throw error;
+		}
+	}
+
+	/**
+	 * Executes the requested code for each item in the input data
+	 */
+	private async runForEachItem(
+		taskId: string,
+		settings: JSExecSettings,
+		allData: AllCodeTaskData,
+		workflow: Workflow,
+		customConsole: CustomConsole,
+	): Promise<INodeExecutionData[]> {
+		const inputItems = allData.connectionInputData;
+		const returnData: INodeExecutionData[] = [];
+
+		for (let index = 0; index < inputItems.length; index++) {
+			const item = inputItems[index];
+			const dataProxy = this.createDataProxy(allData, workflow, index);
+			const context: Context = {
+				require,
+				module: {},
+				console: customConsole,
+				item,
+
+				...dataProxy,
+				...this.buildRpcCallObject(taskId),
+			};
+
+			try {
+				let result = (await runInNewContext(
+					`module.exports = async function() {${settings.code}\n}()`,
+					context,
+				)) as INodeExecutionData | undefined;
+
+				// Filter out null values
+				if (result === null) {
+					continue;
+				}
+
+				result = validateRunForEachItemOutput(result, index);
+				if (result) {
+					returnData.push(
+						result.binary
+							? {
+									json: result.json,
+									pairedItem: { item: index },
+									binary: result.binary,
+								}
+							: {
+									json: result.json,
+									pairedItem: { item: index },
+								},
+					);
+				}
+			} catch (error) {
+				if (!settings.continueOnFail) {
+					(error as Record<string, unknown>).node = allData.node;
+					throw error;
+				}
+
+				returnData.push({
+					json: { error: this.getErrorMessageFromVmError(error) },
+					pairedItem: {
+						item: index,
+					},
+				});
+			}
+		}
+
+		return returnData;
+	}
+
+	private createDataProxy(allData: AllCodeTaskData, workflow: Workflow, itemIndex: number) {
+		return new WorkflowDataProxy(
 			workflow,
 			allData.runExecutionData,
 			allData.runIndex,
-			allData.itemIndex,
+			itemIndex,
 			allData.activeNodeName,
 			allData.connectionInputData,
 			allData.siblingParameters,
-			settings.mode,
+			allData.mode,
 			getAdditionalKeys(
 				allData.additionalData as IWorkflowExecuteAdditionalData,
 				allData.mode,
@@ -113,35 +266,14 @@ export class JsTaskRunner extends TaskRunner {
 			allData.defaultReturnRunIndex,
 			allData.selfData,
 			allData.contextNodeName,
-		);
+		).getDataProxy();
+	}
 
-		const customConsole = {
-			log: (...args: unknown[]) => {
-				const logOutput = args
-					.map((arg) => (typeof arg === 'object' && arg !== null ? JSON.stringify(arg) : arg))
-					.join(' ');
-				console.log('[JS Code]', logOutput);
-				void this.makeRpcCall(task.taskId, 'logNodeOutput', [logOutput]);
-			},
-		};
+	private getErrorMessageFromVmError(error: unknown): string {
+		if (typeof error === 'object' && !!error && 'message' in error) {
+			return error.message as string;
+		}
 
-		const context: Context = {
-			require,
-			module: {},
-			console: customConsole,
-
-			...dataProxy.getDataProxy(),
-			...this.buildRpcCallObject(task.taskId),
-		};
-
-		const result = (await runInNewContext(
-			`module.exports = async function() {${settings.code}\n}()`,
-			context,
-		)) as TaskResultData['result'];
-
-		return {
-			result,
-			customData: allData.runExecutionData.resultData.metadata,
-		};
+		return JSON.stringify(error);
 	}
 }

packages/@n8n/task-runner/src/execution-error.ts

@@ -0,0 +1,84 @@
+import { ApplicationError } from 'n8n-workflow';
+
+export class ExecutionError extends ApplicationError {
+	description: string | null = null;
+
+	itemIndex: number | undefined = undefined;
+
+	context: { itemIndex: number } | undefined = undefined;
+
+	stack = '';
+
+	lineNumber: number | undefined = undefined;
+
+	constructor(error: Error & { stack?: string }, itemIndex?: number) {
+		super(error.message);
+		this.itemIndex = itemIndex;
+
+		if (this.itemIndex !== undefined) {
+			this.context = { itemIndex: this.itemIndex };
+		}
+
+		this.stack = error.stack ?? '';
+
+		this.populateFromStack();
+	}
+
+	/**
+	 * Populate error `message` and `description` from error `stack`.
+	 */
+	private populateFromStack() {
+		const stackRows = this.stack.split('\n');
+
+		if (stackRows.length === 0) {
+			this.message = 'Unknown error';
+		}
+
+		const messageRow = stackRows.find((line) => line.includes('Error:'));
+		const lineNumberRow = stackRows.find((line) => line.includes('Code:'));
+		const lineNumberDisplay = this.toLineNumberDisplay(lineNumberRow);
+
+		if (!messageRow) {
+			this.message = `Unknown error ${lineNumberDisplay}`;
+			return;
+		}
+
+		const [errorDetails, errorType] = this.toErrorDetailsAndType(messageRow);
+
+		if (errorType) this.description = errorType;
+
+		if (!errorDetails) {
+			this.message = `Unknown error ${lineNumberDisplay}`;
+			return;
+		}
+
+		this.message = `${errorDetails} ${lineNumberDisplay}`;
+	}
+
+	private toLineNumberDisplay(lineNumberRow?: string) {
+		const errorLineNumberMatch = lineNumberRow?.match(/Code:(?<lineNumber>\d+)/);
+
+		if (!errorLineNumberMatch?.groups?.lineNumber) return null;
+
+		const lineNumber = errorLineNumberMatch.groups.lineNumber;
+
+		this.lineNumber = Number(lineNumber);
+
+		if (!lineNumber) return '';
+
+		return this.itemIndex === undefined
+			? `[line ${lineNumber}]`
+			: `[line ${lineNumber}, for item ${this.itemIndex}]`;
+	}
+
+	private toErrorDetailsAndType(messageRow?: string) {
+		if (!messageRow) return [null, null];
+
+		const [errorDetails, errorType] = messageRow
+			.split(':')
+			.reverse()
+			.map((i) => i.trim());
+
+		return [errorDetails, errorType === 'Error' ? null : errorType];
+	}
+}

packages/@n8n/task-runner/src/obj-utils.ts

@@ -0,0 +1,5 @@
+export function isObject(maybe: unknown): maybe is { [key: string]: unknown } {
+	return (
+		typeof maybe === 'object' && maybe !== null && !Array.isArray(maybe) && !(maybe instanceof Date)
+	);
+}

packages/@n8n/task-runner/src/result-validation.ts

@@ -0,0 +1,116 @@
+import { normalizeItems } from 'n8n-core';
+import type { INodeExecutionData } from 'n8n-workflow';
+
+import { isObject } from '@/obj-utils';
+import { ValidationError } from '@/validation-error';
+
+export const REQUIRED_N8N_ITEM_KEYS = new Set(['json', 'binary', 'pairedItem', 'error']);
+
+function validateTopLevelKeys(item: INodeExecutionData, itemIndex: number) {
+	for (const key in item) {
+		if (Object.prototype.hasOwnProperty.call(item, key)) {
+			if (REQUIRED_N8N_ITEM_KEYS.has(key)) return;
+
+			throw new ValidationError({
+				message: `Unknown top-level item key: ${key}`,
+				description: 'Access the properties of an item under `.json`, e.g. `item.json`',
+				itemIndex,
+			});
+		}
+	}
+}
+
+function validateItem({ json, binary }: INodeExecutionData, itemIndex: number) {
+	if (json === undefined || !isObject(json)) {
+		throw new ValidationError({
+			message: "A 'json' property isn't an object",
+			description: "In the returned data, every key named 'json' must point to an object.",
+			itemIndex,
+		});
+	}
+
+	if (binary !== undefined && !isObject(binary)) {
+		throw new ValidationError({
+			message: "A 'binary' property isn't an object",
+			description: "In the returned data, every key named 'binary' must point to an object.",
+			itemIndex,
+		});
+	}
+}
+
+/**
+ * Validates the output of a code node in 'Run for All Items' mode.
+ */
+export function validateRunForAllItemsOutput(
+	executionResult: INodeExecutionData | INodeExecutionData[] | undefined,
+) {
+	if (typeof executionResult !== 'object') {
+		throw new ValidationError({
+			message: "Code doesn't return items properly",
+			description: 'Please return an array of objects, one for each item you would like to output.',
+		});
+	}
+
+	if (Array.isArray(executionResult)) {
+		/**
+		 * If at least one top-level key is an n8n item key (`json`, `binary`, etc.),
+		 * then require all item keys to be an n8n item key.
+		 *
+		 * If no top-level key is an n8n key, then skip this check, allowing non-n8n
+		 * item keys to be wrapped in `json` when normalizing items below.
+		 */
+		const mustHaveTopLevelN8nKey = executionResult.some((item) =>
+			Object.keys(item).find((key) => REQUIRED_N8N_ITEM_KEYS.has(key)),
+		);
+
+		if (mustHaveTopLevelN8nKey) {
+			for (let index = 0; index < executionResult.length; index++) {
+				const item = executionResult[index];
+				validateTopLevelKeys(item, index);
+			}
+		}
+	}
+
+	const returnData = normalizeItems(executionResult);
+	returnData.forEach(validateItem);
+	return returnData;
+}
+
+/**
+ * Validates the output of a code node in 'Run for Each Item' mode for single item
+ */
+export function validateRunForEachItemOutput(
+	executionResult: INodeExecutionData | undefined,
+	itemIndex: number,
+) {
+	if (typeof executionResult !== 'object') {
+		throw new ValidationError({
+			message: "Code doesn't return an object",
+			description: `Please return an object representing the output item. ('${executionResult}' was returned instead.)`,
+			itemIndex,
+		});
+	}
+
+	if (Array.isArray(executionResult)) {
+		const firstSentence =
+			executionResult.length > 0
+				? `An array of ${typeof executionResult[0]}s was returned.`
+				: 'An empty array was returned.';
+		throw new ValidationError({
+			message: "Code doesn't return a single object",
+			description: `${firstSentence} If you need to output multiple items, please use the 'Run Once for All Items' mode instead.`,
+			itemIndex,
+		});
+	}
+
+	const [returnData] = normalizeItems([executionResult]);
+
+	validateItem(returnData, itemIndex);
+
+	// If at least one top-level key is a supported item key (`json`, `binary`, etc.),
+	// and another top-level key is unrecognized, then the user mis-added a property
+	// directly on the item, when they intended to add it on the `json` property
+	validateTopLevelKeys(returnData, itemIndex);
+
+	return returnData;
+}

packages/@n8n/task-runner/src/task-runner.ts

@@ -257,11 +257,8 @@ export abstract class TaskRunner {
 			const data = await this.executeTask(task);
 			this.taskDone(taskId, data);
 		} catch (e) {
-			if (ensureError(e)) {
-				this.taskErrored(taskId, (e as Error).message);
-			} else {
-				this.taskErrored(taskId, e);
-			}
+			const error = ensureError(e);
+			this.taskErrored(taskId, error);
 		}
 	}
 

packages/@n8n/task-runner/src/validation-error.ts

@@ -0,0 +1,44 @@
+import { ApplicationError } from 'n8n-workflow';
+
+export class ValidationError extends ApplicationError {
+	description = '';
+
+	itemIndex: number | undefined = undefined;
+
+	context: { itemIndex: number } | undefined = undefined;
+
+	lineNumber: number | undefined = undefined;
+
+	constructor({
+		message,
+		description,
+		itemIndex,
+		lineNumber,
+	}: {
+		message: string;
+		description: string;
+		itemIndex?: number;
+		lineNumber?: number;
+	}) {
+		super(message);
+
+		this.lineNumber = lineNumber;
+		this.itemIndex = itemIndex;
+
+		if (this.lineNumber !== undefined && this.itemIndex !== undefined) {
+			this.message = `${message} [line ${lineNumber}, for item ${itemIndex}]`;
+		} else if (this.lineNumber !== undefined) {
+			this.message = `${message} [line ${lineNumber}]`;
+		} else if (this.itemIndex !== undefined) {
+			this.message = `${message} [item ${itemIndex}]`;
+		} else {
+			this.message = message;
+		}
+
+		this.description = description;
+
+		if (this.itemIndex !== undefined) {
+			this.context = { itemIndex: this.itemIndex };
+		}
+	}
+}

packages/nodes-base/nodes/AiTransform/AiTransform.node.ts

@@ -114,7 +114,7 @@ export class AiTransform implements INodeType {
 			context.items = context.$input.all();
 
 			const Sandbox = JavaScriptSandbox;
-			const sandbox = new Sandbox(context, code, index, this.helpers);
+			const sandbox = new Sandbox(context, code, this.helpers);
 			sandbox.on(
 				'output',
 				workflowMode === 'manual'

packages/nodes-base/nodes/Code/Code.node.ts

@@ -1,3 +1,5 @@
+import { TaskRunnersConfig } from '@n8n/config';
+import set from 'lodash/set';
 import {
 	NodeConnectionType,
 	type CodeExecutionMode,
@@ -7,13 +9,12 @@ import {
 	type INodeType,
 	type INodeTypeDescription,
 } from 'n8n-workflow';
-import set from 'lodash/set';
 import Container from 'typedi';
-import { TaskRunnersConfig } from '@n8n/config';
 
 import { javascriptCodeDescription } from './descriptions/JavascriptCodeDescription';
 import { pythonCodeDescription } from './descriptions/PythonCodeDescription';
 import { JavaScriptSandbox } from './JavaScriptSandbox';
+import { JsTaskRunnerSandbox } from './JsTaskRunnerSandbox';
 import { PythonSandbox } from './PythonSandbox';
 import { getSandboxContext } from './Sandbox';
 import { standardizeOutput } from './utils';
@@ -108,23 +109,17 @@ export class Code implements INodeType {
 		const codeParameterName = language === 'python' ? 'pythonCode' : 'jsCode';
 
 		if (!runnersConfig.disabled && language === 'javaScript') {
-			// TODO: once per item
 			const code = this.getNodeParameter(codeParameterName, 0) as string;
-			const items = await this.startJob<INodeExecutionData[]>(
-				{ javaScript: 'javascript', python: 'python' }[language] ?? language,
-				{
-					code,
-					nodeMode,
-					workflowMode,
-				},
-				0,
-			);
+			const sandbox = new JsTaskRunnerSandbox(code, nodeMode, workflowMode, this);
 
-			return [items];
+			return nodeMode === 'runOnceForAllItems'
+				? [await sandbox.runCodeAllItems()]
+				: [await sandbox.runCodeForEachItem()];
 		}
 
 		const getSandbox = (index = 0) => {
 			const code = this.getNodeParameter(codeParameterName, index) as string;
+
 			const context = getSandboxContext.call(this, index);
 			if (nodeMode === 'runOnceForAllItems') {
 				context.items = context.$input.all();
@@ -133,7 +128,7 @@ export class Code implements INodeType {
 			}
 
 			const Sandbox = language === 'python' ? PythonSandbox : JavaScriptSandbox;
-			const sandbox = new Sandbox(context, code, index, this.helpers);
+			const sandbox = new Sandbox(context, code, this.helpers);
 			sandbox.on(
 				'output',
 				workflowMode === 'manual'
@@ -182,7 +177,7 @@ export class Code implements INodeType {
 			const sandbox = getSandbox(index);
 			let result: INodeExecutionData | undefined;
 			try {
-				result = await sandbox.runCodeEachItem();
+				result = await sandbox.runCodeEachItem(index);
 			} catch (error) {
 				if (!this.continueOnFail()) {
 					set(error, 'node', node);

packages/nodes-base/nodes/Code/ExecutionError.ts

@@ -11,7 +11,7 @@ export class ExecutionError extends ApplicationError {
 
 	lineNumber: number | undefined = undefined;
 
-	constructor(error: Error & { stack: string }, itemIndex?: number) {
+	constructor(error: Error & { stack?: string }, itemIndex?: number) {
 		super(error.message);
 		this.itemIndex = itemIndex;
 
@@ -19,7 +19,7 @@ export class ExecutionError extends ApplicationError {
 			this.context = { itemIndex: this.itemIndex };
 		}
 
-		this.stack = error.stack;
+		this.stack = error.stack ?? '';
 
 		this.populateFromStack();
 	}

packages/nodes-base/nodes/Code/JavaScriptSandbox.ts

@@ -5,6 +5,11 @@ import { ValidationError } from './ValidationError';
 import { ExecutionError } from './ExecutionError';
 import type { SandboxContext } from './Sandbox';
 import { Sandbox } from './Sandbox';
+import {
+	mapItemNotDefinedErrorIfNeededForRunForEach,
+	mapItemsNotDefinedErrorIfNeededForRunForAll,
+	validateNoDisallowedMethodsInRunForEach,
+} from './JsCodeValidator';
 
 const { NODE_FUNCTION_ALLOW_BUILTIN: builtIn, NODE_FUNCTION_ALLOW_EXTERNAL: external } =
 	process.env;
@@ -25,7 +30,6 @@ export class JavaScriptSandbox extends Sandbox {
 	constructor(
 		context: SandboxContext,
 		private jsCode: string,
-		itemIndex: number | undefined,
 		helpers: IExecuteFunctions['helpers'],
 		options?: { resolver?: Resolver },
 	) {
@@ -36,7 +40,6 @@ export class JavaScriptSandbox extends Sandbox {
 					plural: 'objects',
 				},
 			},
-			itemIndex,
 			helpers,
 		);
 		this.vm = new NodeVM({
@@ -49,10 +52,10 @@ export class JavaScriptSandbox extends Sandbox {
 		this.vm.on('console.log', (...args: unknown[]) => this.emit('output', ...args));
 	}
 
-	async runCode(): Promise<unknown> {
+	async runCode<T = unknown>(): Promise<T> {
 		const script = `module.exports = async function() {${this.jsCode}\n}()`;
 		try {
-			const executionResult = await this.vm.run(script, __dirname);
+			const executionResult = (await this.vm.run(script, __dirname)) as T;
 			return executionResult;
 		} catch (error) {
 			throw new ExecutionError(error);
@@ -70,10 +73,7 @@ export class JavaScriptSandbox extends Sandbox {
 			executionResult = await this.vm.run(script, __dirname);
 		} catch (error) {
 			// anticipate user expecting `items` to pre-exist as in Function Item node
-			if (error.message === 'items is not defined' && !/(let|const|var) items =/.test(script)) {
-				const quoted = error.message.replace('items', '`items`');
-				error.message = (quoted as string) + '. Did you mean `$input.all()`?';
-			}
+			mapItemsNotDefinedErrorIfNeededForRunForAll(this.jsCode, error);
 
 			throw new ExecutionError(error);
 		}
@@ -87,7 +87,6 @@ export class JavaScriptSandbox extends Sandbox {
 					message: "The code doesn't return an array of arrays",
 					description:
 						'Please return an array of arrays. One array for the different outputs and one for the different items that get returned.',
-					itemIndex: this.itemIndex,
 				});
 			}
 
@@ -101,30 +100,10 @@ export class JavaScriptSandbox extends Sandbox {
 		);
 	}
 
-	async runCodeEachItem(): Promise<INodeExecutionData | undefined> {
+	async runCodeEachItem(itemIndex: number): Promise<INodeExecutionData | undefined> {
 		const script = `module.exports = async function() {${this.jsCode}\n}()`;
 
-		const match = this.jsCode.match(/\$input\.(?<disallowedMethod>first|last|all|itemMatching)/);
-
-		if (match?.groups?.disallowedMethod) {
-			const { disallowedMethod } = match.groups;
-
-			const lineNumber =
-				this.jsCode.split('\n').findIndex((line) => {
-					return line.includes(disallowedMethod) && !line.startsWith('//') && !line.startsWith('*');
-				}) + 1;
-
-			const disallowedMethodFound = lineNumber !== 0;
-
-			if (disallowedMethodFound) {
-				throw new ValidationError({
-					message: `Can't use .${disallowedMethod}() here`,
-					description: "This is only available in 'Run Once for All Items' mode",
-					itemIndex: this.itemIndex,
-					lineNumber,
-				});
-			}
-		}
+		validateNoDisallowedMethodsInRunForEach(this.jsCode, itemIndex);
 
 		let executionResult: INodeExecutionData;
 
@@ -132,16 +111,13 @@ export class JavaScriptSandbox extends Sandbox {
 			executionResult = await this.vm.run(script, __dirname);
 		} catch (error) {
 			// anticipate user expecting `item` to pre-exist as in Function Item node
-			if (error.message === 'item is not defined' && !/(let|const|var) item =/.test(script)) {
-				const quoted = error.message.replace('item', '`item`');
-				error.message = (quoted as string) + '. Did you mean `$input.item.json`?';
-			}
+			mapItemNotDefinedErrorIfNeededForRunForEach(this.jsCode, error);
 
-			throw new ExecutionError(error, this.itemIndex);
+			throw new ExecutionError(error, itemIndex);
 		}
 
-		if (executionResult === null) return;
+		if (executionResult === null) return undefined;
 
-		return this.validateRunCodeEachItem(executionResult);
+		return this.validateRunCodeEachItem(executionResult, itemIndex);
 	}
 }

packages/nodes-base/nodes/Code/JsCodeValidator.ts

@@ -0,0 +1,54 @@
+import { ValidationError } from './ValidationError';
+
+/**
+ * Validates that no disallowed methods are used in the
+ * runCodeForEachItem JS code. Throws `ValidationError` if
+ * a disallowed method is found.
+ */
+export function validateNoDisallowedMethodsInRunForEach(code: string, itemIndex: number) {
+	const match = code.match(/\$input\.(?<disallowedMethod>first|last|all|itemMatching)/);
+
+	if (match?.groups?.disallowedMethod) {
+		const { disallowedMethod } = match.groups;
+
+		const lineNumber =
+			code.split('\n').findIndex((line) => {
+				return line.includes(disallowedMethod) && !line.startsWith('//') && !line.startsWith('*');
+			}) + 1;
+
+		const disallowedMethodFound = lineNumber !== 0;
+
+		if (disallowedMethodFound) {
+			throw new ValidationError({
+				message: `Can't use .${disallowedMethod}() here`,
+				description: "This is only available in 'Run Once for All Items' mode",
+				itemIndex,
+				lineNumber,
+			});
+		}
+	}
+}
+
+/**
+ * Checks if the error message indicates that `items` is not defined and
+ * modifies the error message to suggest using `$input.all()`.
+ */
+export function mapItemsNotDefinedErrorIfNeededForRunForAll(code: string, error: Error) {
+	// anticipate user expecting `items` to pre-exist as in Function Item node
+	if (error.message === 'items is not defined' && !/(let|const|var) +items +=/.test(code)) {
+		const quoted = error.message.replace('items', '`items`');
+		error.message = (quoted as string) + '. Did you mean `$input.all()`?';
+	}
+}
+
+/**
+ * Maps the "item is not defined" error message to provide a more helpful suggestion
+ * for users who may expect `items` to pre-exist
+ */
+export function mapItemNotDefinedErrorIfNeededForRunForEach(code: string, error: Error) {
+	// anticipate user expecting `items` to pre-exist as in Function Item node
+	if (error.message === 'item is not defined' && !/(let|const|var) +item +=/.test(code)) {
+		const quoted = error.message.replace('item', '`item`');
+		error.message = (quoted as string) + '. Did you mean `$input.item.json`?';
+	}
+}

packages/nodes-base/nodes/Code/JsTaskRunnerSandbox.ts

@@ -0,0 +1,92 @@
+import {
+	ensureError,
+	type CodeExecutionMode,
+	type IExecuteFunctions,
+	type INodeExecutionData,
+	type WorkflowExecuteMode,
+} from 'n8n-workflow';
+
+import { ExecutionError } from './ExecutionError';
+import {
+	mapItemsNotDefinedErrorIfNeededForRunForAll,
+	validateNoDisallowedMethodsInRunForEach,
+} from './JsCodeValidator';
+
+/**
+ * JS Code execution sandbox that executes the JS code using task runner.
+ */
+export class JsTaskRunnerSandbox {
+	constructor(
+		private readonly jsCode: string,
+		private readonly nodeMode: CodeExecutionMode,
+		private readonly workflowMode: WorkflowExecuteMode,
+		private readonly executeFunctions: IExecuteFunctions,
+	) {}
+
+	async runCode<T = unknown>(): Promise<T> {
+		const itemIndex = 0;
+
+		try {
+			const executionResult = (await this.executeFunctions.startJob<T>(
+				'javascript',
+				{
+					code: this.jsCode,
+					nodeMode: this.nodeMode,
+					workflowMode: this.workflowMode,
+				},
+				itemIndex,
+			)) as T;
+			return executionResult;
+		} catch (e) {
+			const error = ensureError(e);
+			throw new ExecutionError(error);
+		}
+	}
+
+	async runCodeAllItems(): Promise<INodeExecutionData[]> {
+		const itemIndex = 0;
+
+		return await this.executeFunctions
+			.startJob<INodeExecutionData[]>(
+				'javascript',
+				{
+					code: this.jsCode,
+					nodeMode: this.nodeMode,
+					workflowMode: this.workflowMode,
+					continueOnFail: this.executeFunctions.continueOnFail(),
+				},
+				itemIndex,
+			)
+			.catch((e) => {
+				const error = ensureError(e);
+				// anticipate user expecting `items` to pre-exist as in Function Item node
+				mapItemsNotDefinedErrorIfNeededForRunForAll(this.jsCode, error);
+
+				throw new ExecutionError(error);
+			});
+	}
+
+	async runCodeForEachItem(): Promise<INodeExecutionData[]> {
+		validateNoDisallowedMethodsInRunForEach(this.jsCode, 0);
+		const itemIndex = 0;
+
+		return await this.executeFunctions
+			.startJob<INodeExecutionData[]>(
+				'javascript',
+				{
+					code: this.jsCode,
+					nodeMode: this.nodeMode,
+					workflowMode: this.workflowMode,
+					continueOnFail: this.executeFunctions.continueOnFail(),
+				},
+				itemIndex,
+			)
+			.catch((e) => {
+				const error = ensureError(e);
+				// anticipate user expecting `items` to pre-exist as in Function Item node
+				mapItemsNotDefinedErrorIfNeededForRunForAll(this.jsCode, error);
+
+				throw new ExecutionError(error);
+			});
+	}
+}

packages/nodes-base/nodes/Code/PythonSandbox.ts

@@ -18,7 +18,6 @@ export class PythonSandbox extends Sandbox {
 	constructor(
 		context: SandboxContext,
 		private pythonCode: string,
-		itemIndex: number | undefined,
 		helpers: IExecuteFunctions['helpers'],
 	) {
 		super(
@@ -28,7 +27,6 @@ export class PythonSandbox extends Sandbox {
 					plural: 'dictionaries',
 				},
 			},
-			itemIndex,
 			helpers,
 		);
 		// Since python doesn't allow variable names starting with `$`,
@@ -39,8 +37,8 @@ export class PythonSandbox extends Sandbox {
 		}, {} as PythonSandboxContext);
 	}
 
-	async runCode(): Promise<unknown> {
-		return await this.runCodeInPython<unknown>();
+	async runCode<T = unknown>(): Promise<T> {
+		return await this.runCodeInPython<T>();
 	}
 
 	async runCodeAllItems() {
@@ -48,9 +46,9 @@ export class PythonSandbox extends Sandbox {
 		return this.validateRunCodeAllItems(executionResult);
 	}
 
-	async runCodeEachItem() {
+	async runCodeEachItem(itemIndex: number) {
 		const executionResult = await this.runCodeInPython<INodeExecutionData>();
-		return this.validateRunCodeEachItem(executionResult);
+		return this.validateRunCodeEachItem(executionResult, itemIndex);
 	}
 
 	private async runCodeInPython<T>() {

packages/nodes-base/nodes/Code/Sandbox.ts

@@ -1,7 +1,8 @@
 import { EventEmitter } from 'events';
 import type { IExecuteFunctions, INodeExecutionData, IWorkflowDataProxyData } from 'n8n-workflow';
-import { ValidationError } from './ValidationError';
+
 import { isObject } from './utils';
+import { ValidationError } from './ValidationError';
 
 interface SandboxTextKeys {
 	object: {
@@ -39,26 +40,28 @@ export function getSandboxContext(this: IExecuteFunctions, index: number): Sandb
 export abstract class Sandbox extends EventEmitter {
 	constructor(
 		private textKeys: SandboxTextKeys,
-		protected itemIndex: number | undefined,
 		protected helpers: IExecuteFunctions['helpers'],
 	) {
 		super();
 	}
 
-	abstract runCode(): Promise<unknown>;
+	abstract runCode<T = unknown>(): Promise<T>;
 
 	abstract runCodeAllItems(): Promise<INodeExecutionData[] | INodeExecutionData[][]>;
 
-	abstract runCodeEachItem(): Promise<INodeExecutionData | undefined>;
+	abstract runCodeEachItem(itemIndex: number): Promise<INodeExecutionData | undefined>;
 
-	validateRunCodeEachItem(executionResult: INodeExecutionData | undefined): INodeExecutionData {
+	validateRunCodeEachItem(
+		executionResult: INodeExecutionData | undefined,
+		itemIndex: number,
+	): INodeExecutionData {
 		if (typeof executionResult !== 'object') {
 			throw new ValidationError({
 				message: `Code doesn't return ${this.getTextKey('object', { includeArticle: true })}`,
 				description: `Please return ${this.getTextKey('object', {
 					includeArticle: true,
 				})} representing the output item. ('${executionResult}' was returned instead.)`,
-				itemIndex: this.itemIndex,
+				itemIndex,
 			});
 		}
 
@@ -70,25 +73,24 @@ export abstract class Sandbox extends EventEmitter {
 			throw new ValidationError({
 				message: `Code doesn't return a single ${this.getTextKey('object')}`,
 				description: `${firstSentence} If you need to output multiple items, please use the 'Run Once for All Items' mode instead.`,
-				itemIndex: this.itemIndex,
+				itemIndex,
 			});
 		}
 
 		const [returnData] = this.helpers.normalizeItems([executionResult]);
 
-		this.validateItem(returnData);
+		this.validateItem(returnData, itemIndex);
 
 		// If at least one top-level key is a supported item key (`json`, `binary`, etc.),
 		// and another top-level key is unrecognized, then the user mis-added a property
 		// directly on the item, when they intended to add it on the `json` property
-		this.validateTopLevelKeys(returnData);
+		this.validateTopLevelKeys(returnData, itemIndex);
 
 		return returnData;
 	}
 
 	validateRunCodeAllItems(
 		executionResult: INodeExecutionData | INodeExecutionData[] | undefined,
-		itemIndex?: number,
 	): INodeExecutionData[] {
 		if (typeof executionResult !== 'object') {
 			throw new ValidationError({
@@ -96,7 +98,6 @@ export abstract class Sandbox extends EventEmitter {
 				description: `Please return an array of ${this.getTextKey('object', {
 					plural: true,
 				})}, one for each item you would like to output.`,
-				itemIndex,
 			});
 		}
 
@@ -113,14 +114,15 @@ export abstract class Sandbox extends EventEmitter {
 			);
 
 			if (mustHaveTopLevelN8nKey) {
-				for (const item of executionResult) {
-					this.validateTopLevelKeys(item);
+				for (let index = 0; index < executionResult.length; index++) {
+					const item = executionResult[index];
+					this.validateTopLevelKeys(item, index);
 				}
 			}
 		}
 
 		const returnData = this.helpers.normalizeItems(executionResult);
-		returnData.forEach((item) => this.validateItem(item));
+		returnData.forEach((item, index) => this.validateItem(item, index));
 		return returnData;
 	}
 
@@ -138,7 +140,7 @@ export abstract class Sandbox extends EventEmitter {
 		return `a ${response}`;
 	}
 
-	private validateItem({ json, binary }: INodeExecutionData) {
+	private validateItem({ json, binary }: INodeExecutionData, itemIndex: number) {
 		if (json === undefined || !isObject(json)) {
 			throw new ValidationError({
 				message: `A 'json' property isn't ${this.getTextKey('object', { includeArticle: true })}`,
@@ -146,7 +148,7 @@ export abstract class Sandbox extends EventEmitter {
 					'object',
 					{ includeArticle: true },
 				)}.`,
-				itemIndex: this.itemIndex,
+				itemIndex,
 			});
 		}
 
@@ -157,18 +159,18 @@ export abstract class Sandbox extends EventEmitter {
 					'object',
 					{ includeArticle: true },
 				)}.`,
-				itemIndex: this.itemIndex,
+				itemIndex,
 			});
 		}
 	}
 
-	private validateTopLevelKeys(item: INodeExecutionData) {
+	private validateTopLevelKeys(item: INodeExecutionData, itemIndex: number) {
 		Object.keys(item).forEach((key) => {
 			if (REQUIRED_N8N_ITEM_KEYS.has(key)) return;
 			throw new ValidationError({
 				message: `Unknown top-level item key: ${key}`,
 				description: 'Access the properties of an item under `.json`, e.g. `item.json`',
-				itemIndex: this.itemIndex,
+				itemIndex,
 			});
 		});
 	}