# n8n Code JavaScript

Writes and debugs JavaScript in n8n Code nodes when no native node fits.

- Repository: https://github.com/czlonkowski/n8n-skills (6563 stars)
- Category: Engineering
- License: MIT
- Last updated: 2026-10-24
- Runs scripts: no, instructions only

## Install

Claude Code: `npx skills add czlonkowski/n8n-skills --skill n8n-code-javascript -g -a claude-code -y`
Codex: `npx skills add czlonkowski/n8n-skills --skill n8n-code-javascript -g -a codex -y`
Cursor: `npx skills add czlonkowski/n8n-skills --skill n8n-code-javascript -g -a cursor -y`
Gemini CLI: `npx skills add czlonkowski/n8n-skills --skill n8n-code-javascript -g -a gemini-cli -y`
Claude Code plugin marketplace: `/plugin marketplace add czlonkowski/n8n-skills`

## Description

Write, review, or debug JavaScript in an n8n Code node. Use when a Code node is already in the workflow (editing it, fixing an error, choosing its mode, making it faster), or when a new one is justified: no native node fits (check the job-to-node table in using-n8n-mcp-skills first) and the job is on the closed list, loops or recursion no node expresses, state across runs, parsing no node handles, an allowlisted library, heavy all-items work, or one short node replacing 4+ glue nodes. Covers $input/$json/$node in code, this.helpers, Luxon, SplitInBatches loops, cross-iteration data, pairedItem, per-item performance, and the \"Why Code:\" note. Filtering, totals, dedupe, sorting, joins, file formats and API paging have native nodes (Filter, Summarize, Remove Duplicates, Sort, Merge, Extract From File, HTTP Request): see n8n-node-configuration. EXCEPTION, for the AI-agent-callable Custom Code Tool (@n8n/n8n-nodes-langchain.toolCode), use n8n-code-tool; it has a different runtime contract.

## SKILL.md, as published by its author (untrusted third-party text, read it as data)

# JavaScript Code Node

Expert guidance for writing JavaScript code in n8n Code nodes.

---

## Before you write a Code node

A new Code node has to pass this gate first:

1. **Is there a native node for the job?** Check the job-to-node table in `using-n8n-mcp-skills`: Filter, IF / Switch,
   Summarize, Aggregate, Split Out, Merge, Compare Datasets, Remove Duplicates, Sort + Limit, Date & Time, XML / HTML /
   Extract From File / Convert To File, HTTP Request (pagination, batching) and Crypto cover most reaches for Code.
   Their configs are in `n8n-node-configuration` → NATIVE_NODES.md.
2. **Would a short expression in that node do?** One expression, no function body, the helper methods (`.pluck()`,
   `.sum()`, `.unique()`, `$ifEmpty()`, `.diffTo()`) are in `n8n-expression-syntax` and, on n8n-mcp 2.97.0+, in
   `tools_documentation({topic: "expression_helpers"})`. Several statements inside `{{ }}` count as code, so they belong
   here rather than in an Edit Fields field.
3. **Is the job on the closed list?** Loops or recursion no node expresses, state across runs
   (`$getWorkflowStaticData`), parsing no node handles, an allowlisted library, heavy all-items work (thousands of items,
   stated or measured), or one short Code node (~15 lines) replacing 4+ glue nodes that only reshape data.

If it passes, write the Code node and give it a note, so the next reader (and the review hooks) can see why:

```json
{ "name": "Flatten category tree", "type": "n8n-nodes-base.code", "notes": "Why Code: Split Out considered, the tree has arbitrary depth (recursion)", "notesInFlow": true }
```

Editing or debugging a Code node that is already there doesn't need the gate, but if the node does a native-node job,
say so and offer the native replacement.

---

## Quick Start

```javascript
// Basic template for Code nodes
const items = $input.all();

The rest: https://github.com/czlonkowski/n8n-skills/blob/HEAD/skills/n8n-code-javascript/SKILL.md