n8n-code-javascript

JavaScript Code Node

Expert guidance for writing JavaScript code in n8n Code nodes.

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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;

Essential Rules

1. Choose "Run Once for All Items" mode (recommended for most use cases)
2. Access data: $input.all(), $input.first(), or $input.item
3. CRITICAL: Must return [{json: {...}}] format
4. CRITICAL: Webhook data is under $json.body (not $json directly)
5. Built-ins available: $helpers.httpRequest(), DateTime (Luxon), $jmespath()

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When NOT to use a Code node (native-first)

Reach for a native node before writing JavaScript — Code nodes are harder to read, review, and they run V8 in-process (OOM risk on large data, see below). In a real production audit, Code nodes outnumbered native conditional nodes ~2.5:1 — much of it avoidable:

If you are doing…	Use this native node, NOT Code
Branching on a condition	IF (2 branches) / Switch (n branches)
Dropping items by a rule	Filter
Setting / renaming / mapping fields	Set (Edit Fields)
Merging / combining streams	Merge
Aggregating into one item	Aggregate / Summarize
Looping over large batches	Loop Over Items (SplitInBatches)

Memory / OOM (real production incident): a Code node that loads or iterates a large dataset — especially a full DB result set (>~10k rows), binary, or file contents — can spike the V8 heap (~3 GB cap) and crash the n8n pod (OOM). For large data: page/limit at the source, process in SplitInBatches, or push the work into the database/native node instead of materializing it all in JS.

Use a Code node when the logic genuinely has no native equivalent (custom parsing, multi-field computation, shaping a bespoke payload).