n8n-code-javascript

# JavaScript Code Node Expert guidance for writing JavaScript code in n8n Code nodes. --- ## Quick Start ```javascript // 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() (no auth), DateTime (Luxon), $jmespath(). **Not available**: $helpers.httpRequestWithAuthentication, $env (when N8N_BLOCK_ENV_ACCESS_IN_NODE=true), require() (unless allowlisted) 6. **Instance-allowlisted libraries**: Self-hosted instances can allowlist modules via `N8N_RUNNERS_ALLOWED_BUILT_IN_MODULES` and `N8N_RUNNERS_ALLOWED_EXTERNAL_MODULES` (legacy: `NODE_FUNCTION_ALLOW_BUILTIN` / `NODE_FUNCTION_ALLOW_EXTERNAL`). If the user says their instance allows specific modules (e.g. `axios`, `lodash`, `crypto`), use them via `require()` — don't refuse. If unsure, ask or default to built-ins only. 7. **Wrong skill?** If you're writing code for a **Custom Code Tool** attached to an AI Agent (`@n8n/n8n-nodes-langchain.toolCode`), stop — that node has a different contract (input via `query`, must return a string, no `$input`/`$helpers`). Use the **n8n-code-tool** skill. --- ## Mode Selection Guide The Code node offers two execution modes. Choose based on your use case: ### Run Once for All Items (Recommended - Default) **Use this mode for:** 95% of use cases - **How it works**: Code executes **once** regardless of input count - **Data access**: `$input.all()` or `items` array - **Best for**: Aggregation, filtering, batch processing, transformations, API calls with all data - **Performance**: Faster for multiple items (single execution) ```javascript // Example: Calculate total from all items const allItems = $input.all(); const total = allItems.reduce((sum, item) => sum + (item.json.amount || 0), 0); return [{ json: { total, count: allItems.length, average: total / allItems.length } }]; ``` **When to use:** - ✅ Comparing items across the dataset - ✅ Calculating totals, averages, or statistics - ✅ Sorting or ranking items - ✅ Deduplication - ✅ Building aggregated reports - ✅ Combining data from multiple items ### Run Once for Each Item **Use this mode for:** Specialized cases only - **How it works**: Code executes **separately** for each input item - **Data access**: `$input.item` or `$item` - **Best for**: Item-specific logic, independent operations, per-item validation - **Performance**: Slower for large datasets (multiple executions) ```javascript // Example: Add processing timestamp to each item const item = $input.item; ret