n8n Code JavaScript

Expert guidance for writing JavaScript in n8n Code nodes.

Based on n8n-skills by Romuald Członkowski

Code Node Modes

Run Once for All Items

Process all items together. Most common mode.

// Access all input items
const items = $input.all();

// Process and return
return items.map(item => ({
  json: {
    ...item.json,
    processed: true
  }
}));

Run Once for Each Item

Process each item separately.

// Access current item
const data = $input.item.json;

// Return single item
return {
  json: {
    ...data,
    processed: true
  }
};

Accessing Data

Current Node Input

// All items
const items = $input.all();

// First item
const first = $input.first();

// Current item (in "each item" mode)
const current = $input.item;

// JSON data
const data = $input.first().json;

Previous Nodes

// From specific node
const nodeData = $node["Node Name"].all();
const firstItem = $node["HTTP Request"].first().json;

// From input (same as previous node)
const inputItems = $input.all();

Execution Context

// Workflow info
const workflowId = $workflow.id;
const workflowName = $workflow.name;

// Execution info
const executionId = $execution.id;

// Environment variables
const apiKey = $env.API_KEY;

// n8n variables
const myVar = $vars.myVariable;

Common Patterns

Transform All Items

const items = $input.all();

return items.map(item => ({
  json: {
    id: item.json.id,
    name: item.json.name.toUpperCase(),
    createdAt: new Date().toISOString()
  }
}));

Filter Items

const items = $input.all();

return items.filter(item => item.json.status === 'active');

Aggregate Data

const items = $input.all();

const total = items.reduce((sum, item) => sum + item.json.amount, 0);
const count = items.length;

return [{
  json: {
    total,
    count,
    average: total / count
  }
}];

Group By

const items = $input.all();

const grouped = {};
for (const item of items) {
  const key = item.json.category;
  if (!grouped[key]) grouped[key] = [];
  grouped[key].push(item.json);
}

return Object.entries(grouped).map(([category, items]) => ({
  json: { category, items, count: items.length }
}));

Fetch External Data

const response = await fetch('https://api.example.com/data', {
  headers: { 'Authorization': `Bearer ${$env.API_TOKEN}` }
});

const data = await response.json();

return [{ json: data }];

Error Handling

const items = $input.all();

return items.map(item => {
  try {
    const parsed = JSON.parse(item.json.rawData);
    return { json: { success: true, data: parsed } };
  } catch (error) {
    return { json: { success: false, error: error.message } };
  }
});

Webhook Data Access

CRITICAL: In Code nodes, webhook data is under .body:

// ❌ Wrong
const message = $input.first().json.message;

// ✅ Correct - webhook data is in body
const message = $input.first().json.body.message;
const headers = $input.first().json.headers;
const query = $input.first().json.query;

Date/Time with Luxon

n8n includes Luxon for dates:

const { DateTime } = require('luxon');

// Current time
const now = DateTime.now();

// Parse date
const date = DateTime.fromISO('2024-01-15');

// Format
const formatted = now.toFormat('yyyy-MM-dd HH:mm:ss');

// Add/subtract
const nextWeek = now.plus({ days: 7 });
const yesterday = now.minus({ days: 1 });

// Compare
const isAfter = now > date;
const diff = now.diff(date, 'days').days;

Binary Data

Access Binary

const items = $input.all();

for (const item of items) {
  if (item.binary?.data) {
    const buffer = await item.binary.data.toBuffer();
    const base64 = buffer.toString('base64');
    // Process binary...
  }
}

Create Binary

const data = { key: 'value' };
const jsonString = JSON.stringify(data, null, 2);
const buffer = Buffer.from(jsonString);

return [{
  json: { fileName: 'data.json' },
  binary: {
    data: await this.helpers.prepareBinaryData(buffer, 'data.json', 'application/json')
  }
}];

Common Mistakes

1. Wrong Return Format

// ❌ Wrong - must return array of objects with json property
return { name: 'John' };

// ✅ Correct
return [{ json: { name: 'John' } }];

2. Not Returning All Items

// ❌ Wrong - returns only first item
const item = $input.first();
return [{ json: item.json }];

// ✅ Correct - process all items
return $input.all().map(item => ({ json: item.json }));

3. Accessing Wrong Data Level

// ❌ Wrong - items don't have .data
const data = items[0].data;

// ✅ Correct - use .json
const data = items[0].json;

4. Missing await for Async

// ❌ Wrong - fetch is async
const response = fetch(url);

// ✅ Correct
const response = await fetch(url);
const data = await response.json();

Available Libraries

Built-in libraries available in Code node:

• luxon - Date/time handling
• lodash - Utility functions
• crypto - Cryptographic functions

const { DateTime } = require('luxon');
const _ = require('lodash');
const crypto = require('crypto');

// Use lodash
const grouped = _.groupBy(items, 'category');

// Use crypto
const hash = crypto.createHash('sha256').update(data).digest('hex');

Best Practices

1. Always return array of { json: {...} } objects
2. Use try/catch for error-prone operations
3. Access webhook data via .body
4. Use Luxon for dates, not raw Date()
5. Validate input data before processing
6. Log sparingly - console.log works but adds overhead

Quick Reference

Based on n8n-skills by Romuald Członkowski • Adapted for Moltbot by fazer.ai