Ep 09: Code Is the Ultimate Weapon — JS/Python Inside the Code Node

Code Node's Role

When visual nodes can't handle your needs (complex transforms, regex, math), Code Node is your ultimate escape hatch.

graph TB
    subgraph "n8n Processing Hierarchy"
        L1[🟢 Built-in Nodes
Set / If / Merge
70% of scenarios]
        L2[🟡 Expressions
double curly json.field
20% of scenarios]
        L3[🔴 Code Node
JS / Python
Remaining 10%]
    end
    
    L1 --> L2 --> L3
    style L3 fill:#ff6d5b,stroke:#e55a4e,color:#fff

1. Two Run Modes

Run Once for All Items (Recommended Default)

// ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
// $input.all() returns all Items — you control iteration
// Best for: aggregation, sorting, dedup, grouping
// ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

const allItems = $input.all();

// Sort by price descending
const sorted = allItems.sort((a, b) => b.json.price - a.json.price);

// Deduplicate by email
const seen = new Set();
const unique = allItems.filter(item => {
  if (seen.has(item.json.email)) return false;
  seen.add(item.json.email);
  return true;
});

return unique;  // Must return Item array

Run Once for Each Item

// ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
// $input.item is "this one Item" — n8n handles iteration
// Best for: per-item transforms with no cross-item dependencies
// ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

const item = $input.item;
const phone = item.json.phone;
const masked = phone.slice(0, 3) + '****' + phone.slice(-4);

return {
  json: {
    ...item.json,
    maskedPhone: masked,
    processedAt: new Date().toISOString()
  }
};

2. Built-in Variables

// ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
// Quick reference table
// ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

// 📌 Current node data
$input.all()               // All input Items
$input.first()             // First Item
$input.item                // Current Item (Each mode)

// 📌 Cross-node reference (⭐ Very powerful!)
$('Set').all()             // All outputs from "Set" node
$('HTTP Request').first().json  // First Item's JSON from another node

// 📌 Workflow metadata
$execution.id              // Current execution ID
$workflow.name             // Workflow name
$now.toISO()               // Current ISO time
$env.MY_SECRET_KEY         // Environment variable (secure!)

3. Practical Examples

CSV Parser

const csv = $input.first().json.csvData;
const lines = csv.split('\n');
const headers = lines[0].split(',');

const items = lines.slice(1).map(line => {
  const values = line.split(',');
  const obj = {};
  headers.forEach((h, i) => { obj[h.trim()] = values[i]?.trim(); });
  return { json: obj };
});
return items;

Group-By Aggregation

const items = $input.all();
const grouped = items.reduce((acc, item) => {
  const city = item.json.city;
  if (!acc[city]) acc[city] = { city, count: 0, total: 0 };
  acc[city].count += 1;
  acc[city].total += item.json.amount;
  return acc;
}, {});

return Object.values(grouped).map(g => ({ json: g }));

Async Fetch

// n8n Code Node natively supports async/await with fetch
const response = await fetch('https://api.github.com/repos/n8n-io/n8n');
const data = await response.json();
return [{ json: { stars: data.stargazers_count } }];

4. Python Mode (n8n 2.0+)

# Switch Language to "Python" in node settings
# Requires N8N_RUNNERS_ENABLED=true (Task Runner)

items = _input.all()
result = []
for item in items:
    data = item["json"]
    result.append({"json": {
        "original": data["name"],
        "uppercased": data["name"].upper(),
        "length": len(data["name"]),
    }})
return result

Security Model

graph TB
    subgraph "Code Node Sandbox"
        Code[💻 Your Code]
        Code -->|"✅ Allowed"| A1[fetch / HTTP]
        Code -->|"✅ Allowed"| A2[JSON ops]
        Code -->|"❌ Blocked"| D1[File system access]
        Code -->|"❌ Blocked"| D2[require external modules]
        Code -->|"❌ Blocked"| D3[child_process]
    end
    
    style Code fill:#ff6d5b,stroke:#e55a4e,color:#fff

Next Episode

In Ep 10, we'll speed-run n8n's most useful built-in utility nodes — Merge, Set, Edit Image, Date & Time — completing the everyday developer toolkit.