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(), DateTime (Luxon), $jmespath()

---

## 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
- **Pe