n8n-code-javascript

JavaScript Code Node

Expert guidance for writing JavaScript code in n8n Code nodes.

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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:

{ "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.

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Quick Start

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

// Process data
const processed = items.map(item => ({
  json: {
    ...item.json,
    processed: true,
    timestamp: new Date().toISOString()
  }
}));

return processed;