n8n Code node: JavaScript, Python, item modes and common errors

Mindket editors · Published November 4, 2026 · Updated November 5, 2026 · 9 min read

A black banner titled "n8n advanced" over the line "Errors, sub-workflows, code and scaling".

The n8n Code node runs your own JavaScript or Python as a workflow step. In the default mode, Run Once for All Items, your code runs once over every input item, while the each-item mode runs it once per item. Either way it must return items as objects with a json key, and it cannot make HTTP requests, read files or use credentials.

In this lesson

Pick Run Once for All Items or Run Once for Each Item and return the right shape from each.
Read input with $input, $json and $('Node name') inside the node.
Keep item linking intact with pairedItem when you create new items.
Know what the node cannot do and read its common errors.

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On this page

Before you start
Write your first Code node
Two modes, two return shapes
Reading data from the input and from other nodes
Python in the Code node
Keep item linking intact
What the Code node cannot do
What the maker of n8n-skills and Samir Saci say about Code node languages
Common mistakes
Try it yourself
What to learn next
Check yourself
Frequently asked questions
Sources

Before you start

The Code node changed a good deal across the 2026 releases, so check your version first. The docs say it replaced the Function and Function Item nodes from n8n 0.198.0. n8n 3.0, in early access since 27 October 2026, removes those legacy nodes. The breaking-changes page maps them across: Run Once for All Items replaces Function and Run Once for Each Item replaces Function Item. The same release removes the Ask AI tab, and code it generated earlier stays and keeps running.

Python moved too. n8n 2.0 removed the Pyodide version, and native Python on task runners arrived in n8n 1.111.0 and is stable as of n8n 2. The samples here are our own, written from the variable names and item shape in the docs.

Write your first Code node

Every item that leaves the node is an object with a json key. The sample below builds new items from the name field of each input item and sets pairedItem, which a later section explains:

// Mode: Run Once for All Items
const rows = $input.all();
const out = [];
for (let i = 0; i < rows.length; i++) {
  out.push({
    json: { name: rows[i].json.name, nameLength: rows[i].json.name.length },
    pairedItem: i,
  });
}
return out;

Add a Code node after a node that outputs items with a name field, such as an Edit Fields node.
Set Language to JavaScript and Mode to Run Once for All Items, which is the default.
Paste the sample into the code editor.
Select Execute step. The output should hold one item per input item, each with name and nameLength.
Add console.log(rows.length) above the return, run the node again and open your browser's developer console. The cookbook page says console.log() in the Code node writes there.

Two modes, two return shapes

n8n passes data between nodes as an array of objects, each wrapping its data in a json key. The data structure page adds that from n8n 0.166.0 the Code node supplies a missing json key and the array wrapper for you, so a plain object works too. Spelling both out keeps your code honest about what it returns.

The JavaScript task runner's source settles what each mode accepts. Run Once for Each Item runs the code once per input item and expects one item back. Returning null skips that item, and n8n sets pairedItem to the current index for you. This is the each-item version of the sample above:

// Mode: Run Once for Each Item
return { json: { name: $json.name, nameLength: $json.name.length } };

From the Code node page, the reference page and the task runner's source.
Aspect	Run Once for All Items	Run Once for Each Item
How often the code runs	Once, however many input items arrive	Once for every input item
Read input with	`$input.all()`, `$input.first()`, `$input.last()`	`$input.item` or `$json`
Return	An array of items	One item
Returning `null`	No items come out	That item is skipped
Item linking	You set `pairedItem` on new items	n8n sets `pairedItem` to the current index

Reading data from the input and from other nodes

The reference page lists what works in the Code node. Type $ in the editor and n8n suggests the rest. Binary data has its own rule: $binary is not available here, so call this.helpers.getBinaryDataBuffer(itemIndex, binaryPropertyName), which the cookbook page prefers to reaching into items[0].binary.data.data. It is not supported in Python.

One trap sits between the expressions editor and the Code node. The Code node runs plain JavaScript against native Luxon, not n8n's expression engine, and the shortcuts page says what follows.

From the reference page, each entry marked as available in the Code node.
Expression	What you get
`$input.all()`	Every input item
`$input.first()`, `$input.last()`	The first or last input item
`$input.item`	The item being processed
`$json`	Shorthand for `$input.item.json`, available when running once for each item
`$('Node name').all()`, `.first()`, `.last()`	Items from another node, with optional `branchIndex` and `runIndex` arguments
`$('Node name').item`	The item in that node that produced the current one
`$('Node name').itemMatching(i)`	Use it in place of `.item` when you trace back from an input item
`$input.context.noItemsLeft`	A boolean that exists only with Loop Over Items

Python in the Code node

Set Language to Python and you get native Python from task runners. The docs call the move from Pyodide a breaking change, so old scripts may need edits. The same sample in native Python:

# Mode: Run Once for All Items, native Python
rows = []
for item in _items:
    rows.append({"json": {"name": item["json"]["name"]}})
return rows

Only _items in all-items mode and _item in each-item mode exist. The other n8n built-in methods and variables are not supported.
Fields need bracket access, as in item["json"]["my_new_field"]. The dot form item.json.myNewField is not accepted.
On self-hosted n8n, imports work only for standard library and third-party modules that the n8nio/runners image includes and allowlists. On n8n Cloud, no imports are allowed.
Insecure built-ins are denied by default, and type() is on the list. Use print(_items) to inspect data instead.

Keep item linking intact

Most nodes link each output item to the input item that produced it, and later nodes follow that chain with $('Node name').item. In the Code node n8n handles linking for a single item. With more than one incoming item you supply it yourself when you add or return new items, by setting pairedItem to the index of the input item. That is why the first sample carried pairedItem: i.

Going back is the job of itemMatching. This is the docs' example, which restores an email address that an Edit Fields node had dropped:

for(let i=0; i<$input.all().length; i++) {
	$input.all()[i].json.restoreEmail = $('Customer Datastore (n8n training)').itemMatching(i).json.email;
}
return $input.all();

What the Code node cannot do

Task runners execute the code. The docs call them the only isolation layer between user-provided code and n8n, say internal mode is deprecated and point production instances at external mode, with a runners container beside n8n. The self-hosting lesson covers the Docker side.

The timeout changed too. The task runner variables page still lists a default of 300 seconds for N8N_RUNNERS_TASK_TIMEOUT. The breaking changes drop it to 60, so a longer task fails unless you set the variable yourself.

Three numbers behind these limits

seconds a Code node task may run in n8n 3.0 before it fails, down from 300

Source: n8n Docs: v3.0 breaking changes (read November 5, 2026)

modules n8n Cloud lets a JavaScript Code node import, crypto and moment

Source: n8n Docs: Code node (read November 4, 2026)

6.6k

GitHub stars on n8n-skills, a set of Claude Code skills with two for the Code node

Source: Romuald Członkowski on GitHub: n8n-skills (read November 5, 2026)

From the Code node page, its common issues and the module setup page.
You want to	What the Code node does	Use instead
Make an HTTP request	Not available	The HTTP Request node
Read or write a file	Not available	The Read/Write Files from Disk node
Use a credential	Not available by design, and `this.getCredentials()` fails	The HTTP Request node, which supports credentials
Import an npm module on self-hosted n8n	Blocked until you allow it	`NODE_FUNCTION_ALLOW_BUILTIN` and `NODE_FUNCTION_ALLOW_EXTERNAL`, set on the task runners when you use them
Import an npm module on n8n Cloud	Not possible	The two modules n8n provides, crypto and moment

What the maker of n8n-skills and Samir Saci say about Code node languages

Romuald Członkowski, who works at AiAdvisors in Warsaw, built n8n-skills, a set of Claude Code skills for building n8n workflows. Its Python skill gives blunt advice: use JavaScript for 95% of use cases. The reasons it lists match the Python section above. Native Python sees only _items or _item, read as dicts, and the skill calls the import allowlist its critical limitation.

So write Code nodes in JavaScript by default, and keep Python for a self-hosted instance where the module you need is already allowed.

The n8n team shared a post by Samir Saci on X on 2 October 2025, about moving from Python to JavaScript in n8n. Saci, who describes himself as the founder of LogiGreen, used Code nodes for sales analytics and built ABC and Pareto charts. A port like his starts in Run Once for All Items, because a Pareto chart needs every row at once.

Use JavaScript for 95% of use cases

Romuald Członkowski, Creator of n8n-skills, AiAdvisors · GitHub (read November 5, 2026)

n8n.io (@n8n_io) on X, 2 October 2025. Great post by @Samir_Saci_ on moving from Python to JavaScript in n8n. He shows how to use Code nodes for sales analytics, build ABC and Pareto charts, and compare with FastAPI. — n8n.io on X, 2 October 2025

A screenshot of X's own embed of the post, taken on 5 November 2026, with the time in UTC. Select it to open the post on X.

Common mistakes

"Code doesn't return items properly" and "Code doesn't return an object". The node must return an array of objects that wrap their data in json. A script that ends without a return, or returns undefined, lands here, as the common issues page explains.
"A 'json' property isn't an object". You set json to an array. Put the array inside an object, such as { json: { rows } }.
"'import' and 'export' may only appear at the top level". The sandbox does not support them, so use require(), and on a self-hosted install allow the module first.
"Cannot find module". Install the module into your n8n environment, and with Docker extend the official image. Then set NODE_FUNCTION_ALLOW_BUILTIN or NODE_FUNCTION_ALLOW_EXTERNAL. With external task runners, set them in the runners config file instead.
Calling $getCredentials() or this.getCredentials(). It fails by design, so move the authenticated call to an HTTP Request node.
Calling $evaluateExpression(). n8n 3.0 removed it from the JavaScript Code node, and secure-mode runners, the default since n8n 2.0, already fail on it. Evaluate the expression in a field of an earlier node and read the result.
Running the node over huge data. The memory page includes "Avoid using the Code node where possible" in its tips for cutting memory use.

Try it yourself

Run the all-items sample, then the each-item sample on the same input, and compare the output items.
In the each-item sample, return null for items with no name and count how many items come out.
Add console.log($input.first()) and read the browser console while you run the node.
If you self-host, allow one built-in module with NODE_FUNCTION_ALLOW_BUILTIN=crypto, load it with require() and hash a field.

What to learn next

The Code node runs on task runners, and each worker in a scaled setup needs its own. Lesson 4 puts n8n into queue mode, with Redis, workers and the settings that decide how much runs at once. For the bigger picture of what n8n nodes can do before you reach for code, what is n8n is the place to start.

Check yourself

You use Run Once for Each Item. What should the code return?
Show answer
B. One item, such as { json: { ... } } Each-item mode runs the code once per input item and expects one item back, and null skips that item.
The Code node cannot reach credentials. Which node makes an authenticated API call?
Show answer
D. HTTP Request The HTTP Request node supports credentials, which the Code node cannot access by design.
In native Python in the Code node, how do you read the name field of an input item?
Show answer
A. item["json"]["name"] Native Python accepts only bracket access, and the dot form works in the retired Pyodide version.
In Run Once for All Items mode you create new items that later nodes must trace back. What do you set on each?
Show answer
C. pairedItem New items are linked to no input unless you set pairedItem to the index of the input item.

Frequently asked questions

Can the n8n Code node make HTTP requests?

No. The docs say you can't access the file system or make HTTP requests in the Code node. Use the HTTP Request node, which also supports credentials, and the Read/Write Files from Disk node.

Can I use npm packages in the Code node?

On self-hosted n8n, yes: NODE_FUNCTION_ALLOW_BUILTIN takes built-in module names, NODE_FUNCTION_ALLOW_EXTERNAL takes npm packages, and commas separate several names. With external task runners you set them on the runners. On n8n Cloud you cannot import external modules, and only crypto and moment are available.

Can I import Python libraries in the Code node?

Not on n8n Cloud, where the Python option allows no imports at all. Self-hosters can add libraries to the n8nio/runners image and allowlist them, and the docs say the n8n team is committed to allowing arbitrary libraries securely in the long term.

Do old Function nodes still run after upgrading?

No. A workflow that uses a removed node fails when it runs, and a published one does not activate when n8n starts, so its triggers stop firing. Before you upgrade, Settings, then Migration Report, lists the affected workflows.

Why does my Code node complain about json?

Because json holds something other than an object, most often an array. Wrap the array in an object, such as { json: { rows } }. n8n adds a missing json key and the outer array for you, but it cannot fix a json that is itself an array.

How do I debug code in the Code node?

Use console.log() in JavaScript or print() in Python, then open your browser's developer console and run the node. In native Python you can print _items or _item directly.

Sources

n8n Docs: Code node (read November 4, 2026)https://docs.n8n.io/integrations/builtin/core-nodes/n8n-nodes-base.code
n8n Docs: Using the Code node (read November 4, 2026)https://docs.n8n.io/build/code-in-n8n/using-the-code-node
n8n Docs: Code node common issues (read November 4, 2026)https://docs.n8n.io/integrations/builtin/core-nodes/n8n-nodes-base.code/common-issues
n8n Docs: Enable modules in Code node (read November 4, 2026)https://docs.n8n.io/deploy/host-n8n/configure-n8n/basic-configuration/configuration-examples/enable-modules-in-code-node
n8n Docs: Understand n8n's data structure (read November 4, 2026)https://docs.n8n.io/build/work-with-data/understand-n8ns-data-structure
n8n Docs: Reference previous nodes (read November 4, 2026)https://docs.n8n.io/build/work-with-data/reference-data/reference-previous-nodes
n8n Docs: Use built-in shortcuts (read November 4, 2026)https://docs.n8n.io/build/code-in-n8n/use-built-in-shortcuts
n8n Docs: Output to the browser console (read November 4, 2026)https://docs.n8n.io/build/code-in-n8n/cookbook/code-node/output-to-the-browser-console
n8n Docs: Get the binary data buffer (read November 4, 2026)https://docs.n8n.io/build/code-in-n8n/cookbook/code-node/get-the-binary-data-buffer
n8n Docs: Accessing linked items in the Code node (read November 4, 2026)https://docs.n8n.io/build/work-with-data/reference-data/link-data-items/accessing-linked-items-in-the-code-node
n8n Docs: Preserving linking in the Code node (read November 4, 2026)https://docs.n8n.io/build/work-with-data/reference-data/link-data-items/preserving-linking-in-the-code-node
n8n Docs: Set up task runners (read November 4, 2026)https://docs.n8n.io/deploy/host-n8n/configure-n8n/set-up-task-runners
n8n Docs: Task runner environment variables (read November 4, 2026)https://docs.n8n.io/deploy/host-n8n/configure-n8n/basic-configuration/use-environment-variables/task-runners
n8n Docs: Fix memory issues (read November 4, 2026)https://docs.n8n.io/deploy/host-n8n/configure-n8n/scaling/fix-memory-issues
n8n Docs: v3.0 breaking changes (read November 5, 2026)https://docs.n8n.io/changelog/v30-breaking-changes
n8n repository: JavaScript task runner (js-task-runner.ts) (read November 4, 2026)https://github.com/n8n-io/n8n/blob/master/packages/@n8n/task-runner/src/js-task-runner/js-task-runner.ts
Romuald Członkowski on GitHub: n8n-skills (read November 5, 2026)https://github.com/czlonkowski/n8n-skills
n8n.io on X: great post by Samir Saci on moving from Python to JavaScript in n8n, 2 October 2025 (read November 5, 2026)https://x.com/n8n_io/status/1973659279413403874

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