JavaScript Code Nodes

Expert guidance for writing JavaScript code in n8n Code nodes.

Quick Start Template

// Basic Code node template (Run Once for All Items mode)
const items = $input.all();

// Process data
const processed = items.map(item => ({
  json: {
    ...item.json,
    processed: true,
    timestamp: new Date().toISOString()
  }
}));

return processed;

Essential rules:

Choose “Run Once for All Items” mode (recommended for 95% of use cases)
Access data via $input.all(), $input.first(), or $input.item
Must return [{json: {...}}] format — array of objects with a json key
Webhook data is under $json.body (not $json directly)
Built-ins available: $helpers.httpRequest(), DateTime (Luxon), $jmespath()

Webhook data is nested under .body, not at the root.This is the most common Code node mistake.

// ❌ WRONG — returns undefined
const name = $json.name;
const email = $json.email;

// ✅ CORRECT — webhook data is under .body
const name = $json.body.name;
const email = $json.body.email;

// Also correct using $input
const webhookData = $input.first().json.body;
const name = webhookData.name;

Mode Selection

Run Once for All Items (recommended)
Run Once for Each Item

Use for 95% of use cases.

Code executes once regardless of input count
Access data via $input.all() or the items array
Best for: aggregation, filtering, batch processing, transformations
Faster for multiple items (single execution)

// 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, statistics, sorting or ranking, deduplication, and building aggregated reports.

Use for specialized cases only.

Code executes separately for each input item
Access data via $input.item or $item
Best for: per-item validation with different error handling
Slower for large datasets

// Example: Add processing timestamp to each item
const item = $input.item;

return [{
  json: {
    ...item.json,
    processed: true,
    processedAt: new Date().toISOString()
  }
}];

When to use:

Each item needs an independent API call
Item-specific transformations based on item properties
When items must be processed separately for business reasons

Decision shortcut: Need to look at multiple items? Use “All Items”. Each item completely independent? Use “Each Item”. Not sure? Use “All Items”.

Data Access Patterns

// Pattern 1: $input.all() — most common
const allItems = $input.all();
const valid = allItems.filter(item => item.json.status === 'active');

// Pattern 2: $input.first() — single object
const firstItem = $input.first();
const data = firstItem.json;

// Pattern 3: $input.item — Each Item mode only
const currentItem = $input.item;  // Only in "Each Item" mode

// Pattern 4: $node — reference a specific earlier node
const webhookData = $node["Webhook"].json;       // from Webhook node
const httpData = $node["HTTP Request"].json;    // from HTTP Request node

Return Format Requirements

Always return an array of objects with a json property. Any other format causes the workflow to fail.

// ✅ Single result
return [{
  json: {
    field1: value1,
    field2: value2
  }
}];

// ✅ Multiple results
return [
  {json: {id: 1, data: 'first'}},
  {json: {id: 2, data: 'second'}}
];

// ✅ Transformed array from $input.all()
const transformed = $input.all()
  .filter(item => item.json.valid)
  .map(item => ({
    json: {
      id: item.json.id,
      processed: true
    }
  }));
return transformed;

// ✅ Empty result
return [];

// ❌ WRONG — object without array wrapper
return {
  json: {field: value}
};

// ❌ WRONG — array without json wrapper
return [{field: value}];

// ❌ WRONG — plain string
return "processed";

// ❌ WRONG — raw $input.all() without mapping
return $input.all();  // Missing .map() to add json wrapper

Built-in Functions

`$helpers.httpRequest()`

Make HTTP requests from within a Code node:

const response = await $helpers.httpRequest({
  method: 'GET',
  url: 'https://api.example.com/data',
  headers: {
    'Authorization': 'Bearer token',
    'Content-Type': 'application/json'
  }
});

return [{json: {data: response}}];

`DateTime` (Luxon)

Date and time operations using the Luxon library:

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

// Format dates
const formatted = now.toFormat('yyyy-MM-dd');    // 2025-03-20
const iso = now.toISO();                          // 2025-03-20T14:30:45.000Z

// Date arithmetic
const tomorrow = now.plus({days: 1});
const lastWeek = now.minus({weeks: 1});
const nextMonth = now.plus({months: 1});

// Format result
return [{
  json: {
    today: formatted,
    tomorrow: tomorrow.toFormat('yyyy-MM-dd'),
    oneWeekAgo: lastWeek.toFormat('yyyy-MM-dd')
  }
}];

`$jmespath()`

Query and filter JSON structures:

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

// Filter array (users aged 18+)
const adults = $jmespath(data, 'users[?age >= `18`]');

// Extract a single field from every array element
const names = $jmespath(data, 'users[*].name');

// Nested filtering
const activeAdmins = $jmespath(data, 'users[?role == `admin` && active == `true`]');

return [{json: {adults, names, activeAdmins}}];

Top 5 Error Patterns

#1: Empty code or missing return (most common)

// ❌ WRONG: No return statement
const items = $input.all();
const total = items.reduce((sum, i) => sum + i.json.amount, 0);
// Forgot to return!

// ✅ CORRECT: Always return
const items = $input.all();
const total = items.reduce((sum, i) => sum + i.json.amount, 0);
return [{json: {total}}];

#2: Using n8n expression syntax in code

// ❌ WRONG: {{ }} is for expression fields, not Code nodes
const value = "{{ $json.field }}";
const name = '={{$json.body.name}}';

// ✅ CORRECT: Direct JavaScript access
const value = $json.field;
const name = $json.body.name;

// ✅ ALSO CORRECT: Template literal (for interpolation)
const message = `Hello ${$json.body.name}!`;

#3: Incorrect return wrapper

// ❌ WRONG: Object without array
return {json: {result: 'success'}};

// ❌ WRONG: Array without json wrapper
return [{result: 'success'}];

// ✅ CORRECT
return [{json: {result: 'success'}}];

#4: Missing null / undefined checks

// ❌ WRONG: Crashes if user or email doesn't exist
const email = item.json.user.email;

// ✅ CORRECT: Optional chaining with default
const email = item.json?.user?.email || 'no-email@example.com';

// ✅ ALSO CORRECT: Explicit guard clause
if (!item.json.user) {
  return [];
}
const email = item.json.user.email;

#5: Webhook body nesting

// ❌ WRONG: Webhook data is not at $json root
const email = $json.email;
const name = $json.name;

// ✅ CORRECT: Webhook data is under .body
const email = $json.body.email;
const name = $json.body.name;

// ✅ ALSO CORRECT: Using $input
const body = $input.first().json.body;
const email = body.email;

10 Production-Tested Patterns

1. Data transformation and field mapping

const items = $input.all();

return items.map(item => {
  const data = item.json;
  const nameParts = (data.name || '').split(' ');

  return {
    json: {
      first_name: nameParts[0] || '',
      last_name: nameParts.slice(1).join(' '),
      email: (data.email || '').toLowerCase(),
      created_at: new Date().toISOString()
    }
  };
});

2. Aggregation and reporting

const items = $input.all();
const total = items.reduce((sum, item) => sum + (item.json.amount || 0), 0);
const validItems = items.filter(item => (item.json.amount || 0) > 0);

return [{
  json: {
    total,
    count: validItems.length,
    average: validItems.length > 0 ? total / validItems.length : 0,
    timestamp: new Date().toISOString()
  }
}];

3. Top-N filtering and ranking

const items = $input.all();

const topItems = items
  .sort((a, b) => (b.json.score || 0) - (a.json.score || 0))
  .slice(0, 10);

return topItems.map(item => ({json: item.json}));

4. Multi-source data aggregation

const allItems = $input.all();
const results = [];

for (const item of allItems) {
  const sourceName = item.json.source || 'Unknown';

  if (sourceName === 'API1' && item.json.data) {
    results.push({
      json: {
        title: item.json.data.title,
        source: 'API1',
        normalizedAt: new Date().toISOString()
      }
    });
  } else if (sourceName === 'API2' && item.json.record) {
    results.push({
      json: {
        title: item.json.record.name,
        source: 'API2',
        normalizedAt: new Date().toISOString()
      }
    });
  }
}

return results;

5. Regex filtering and extraction

const items = $input.all();
const emailPattern = /\b[A-Za-z0-9._%+-]+@[A-Za-z0-9.-]+\.[A-Z|a-z]{2,}\b/g;

const allEmails = [];
for (const item of items) {
  const text = item.json.text || '';
  const found = text.match(emailPattern);
  if (found) allEmails.push(...found);
}

// Deduplicate
const uniqueEmails = [...new Set(allEmails)];

return [{json: {emails: uniqueEmails, count: uniqueEmails.length}}];

6. HTTP request with error handling

try {
  const response = await $helpers.httpRequest({
    method: 'POST',
    url: 'https://api.example.com/data',
    headers: {'Content-Type': 'application/json'},
    body: JSON.stringify({key: 'value'})
  });

  return [{json: {success: true, data: response}}];
} catch (error) {
  return [{
    json: {
      success: false,
      error: error.message,
      timestamp: new Date().toISOString()
    }
  }];
}

7. Date manipulation with Luxon

const items = $input.all();

return items.map(item => {
  const createdAt = item.json.created_at;
  const date = DateTime.fromISO(createdAt);

  return {
    json: {
      ...item.json,
      formatted_date: date.toFormat('MMMM dd, yyyy'),
      days_ago: Math.floor(DateTime.now().diff(date, 'days').days),
      is_recent: DateTime.now().diff(date, 'days').days < 7
    }
  };
});

8. Deduplication

const items = $input.all();
const seen = new Set();

const unique = items.filter(item => {
  const key = item.json.email || item.json.id;
  if (seen.has(key)) return false;
  seen.add(key);
  return true;
});

return unique.map(item => ({json: item.json}));

9. Data validation and cleaning

const items = $input.all();

const validated = items.map(item => {
  const data = item.json;
  const errors = [];

  if (!data.email || !data.email.includes('@')) errors.push('Invalid email');
  if (!data.name || data.name.trim().length === 0) errors.push('Name required');

  return {
    json: {
      ...data,
      name: (data.name || '').trim(),
      email: (data.email || '').toLowerCase().trim(),
      valid: errors.length === 0,
      validation_errors: errors.length > 0 ? errors : null
    }
  };
});

return validated;

10. Combining data from multiple nodes

// Access data from multiple earlier nodes
const webhookBody = $node["Webhook"].json.body;
const apiResponse = $node["HTTP Request"].json;

return [{
  json: {
    user_id: webhookBody.user_id,
    user_name: webhookBody.name,
    api_data: apiResponse.data,
    combined_at: new Date().toISOString()
  }
}];

Best Practices

// 1. Validate input first
const items = $input.all();
if (!items || items.length === 0) return [];

// 2. Use try-catch for HTTP requests
try {
  const response = await $helpers.httpRequest({url: '...'});
  return [{json: {success: true, data: response}}];
} catch (error) {
  return [{json: {success: false, error: error.message}}];
}

// 3. Prefer functional array methods
// ✅ Good
const processed = $input.all()
  .filter(item => item.json.valid)
  .map(item => ({json: {id: item.json.id}}));

// 4. Filter early, process late
// ✅ Good — filter first to reduce work
const processed = $input.all()
  .filter(item => item.json.status === 'active')  // Reduce first
  .map(item => expensiveTransformation(item));     // Then transform

// 5. Debug with console.log
console.log(`Processing ${items.length} items`);
console.log('First item:', items[0]?.json);

When to Use a Code Node

Use Code Node	Use Another Node Instead
Complex multi-step transformations	Simple field mapping → Set node
Custom business logic	Basic filtering → Filter node
Aggregation across items	Simple conditions → IF / Switch node
API response parsing with complex structure	HTTP requests only → HTTP Request node
Recursive operations

Pre-Deploy Checklist

Code is not empty — has meaningful logic
Return statement exists
Return format is [{json: {...}}]
Data access uses $input.all(), $input.first(), or $input.item
No {{ }} expressions — using direct JavaScript access
Null/undefined guards with optional chaining (?.) or defaults
Webhook data accessed via .body if input is from a Webhook node
Mode is “All Items” unless per-item isolation is required
All code paths return the same structure

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JavaScript Code Nodes

JavaScript Code Nodes

Quick Start Template

Mode Selection

Data Access Patterns

Return Format Requirements

Built-in Functions

`$helpers.httpRequest()`

`DateTime` (Luxon)

`$jmespath()`

Top 5 Error Patterns

10 Production-Tested Patterns

Best Practices

When to Use a Code Node

Pre-Deploy Checklist

​JavaScript Code Nodes

​Quick Start Template

​Mode Selection

​Data Access Patterns

​Return Format Requirements

​Built-in Functions

​$helpers.httpRequest()

​DateTime (Luxon)

​$jmespath()

​Top 5 Error Patterns

​10 Production-Tested Patterns

​Best Practices

​When to Use a Code Node

​Pre-Deploy Checklist

JavaScript Code Nodes

Quick Start Template

Mode Selection

Data Access Patterns

Return Format Requirements

Built-in Functions

`$helpers.httpRequest()`

`DateTime` (Luxon)

`$jmespath()`

Top 5 Error Patterns

10 Production-Tested Patterns

Best Practices

When to Use a Code Node

Pre-Deploy Checklist