n8n 03 — Data & Expressions

Data in n8n flows as an array of items. Each item has two parts:

// A typical item structure
{
  json: {
    id: 42,
    name: "Alice",
    email: "alice@example.com",
    score: 95
  },
  binary: {
    // optional: file attachments, images, etc.
    data: { mimeType: "image/png", data: "base64string..." }
  }
}

When an HTTP Request returns an array of 10 users, n8n creates 10 items — one per user. Most nodes process each item individually in a loop.

Expressions use double curly braces {{ }} and give you access to dynamic data. Click the lightning bolt icon next to any field to switch from a static value to an expression.

# Access current item fields
{{ $json.name }}
{{ $json.user.email }}
{{ $json["field-with-dashes"] }}

# Access a specific node's output
{{ $node["HTTP Request"].json.id }}
{{ $('Fetch Users').item.json.email }}

# Access item by position
{{ $('Fetch Users').first().json.name }}
{{ $('Fetch Users').last().json.name }}

# Modern syntax (n8n v1+)
{{ $('NodeName').item.json.field }}
{{ $('NodeName').all()[0].json.field }}

# Legacy syntax (still works)
{{ $node["NodeName"].json.field }}

# Example: get the ID from step 2 while in step 4
{{ $('Fetch Product').item.json.product_id }}

# Access response from HTTP Request node
{{ $('Call API').item.json.data.users[0].name }}

n8n uses Luxon for date handling. $now and $today are Luxon DateTime objects.

# Format dates
{{ $now.toISO() }}                      # "2024-06-15T09:30:00.000Z"
{{ $now.toFormat('yyyy-MM-dd') }}       # "2024-06-15"
{{ $now.toFormat('dd/MM/yyyy HH:mm') }} # "15/06/2024 09:30"

# Date arithmetic
{{ $now.minus({ days: 7 }).toISO() }}   # 7 days ago
{{ $now.plus({ hours: 2 }).toISO() }}   # 2 hours from now
{{ $now.startOf('month').toISO() }}     # First day of month
{{ $now.endOf('week').toISO() }}        # End of current week

# Parse an existing date string
{{ DateTime.fromISO($json.created_at).toFormat('MMM d, yyyy') }}
{{ DateTime.fromFormat($json.date, 'dd/MM/yyyy').toISO() }}

# Standard JavaScript string methods
{{ $json.name.toUpperCase() }}           # "ALICE"
{{ $json.name.toLowerCase() }}           # "alice"
{{ $json.email.split('@')[1] }}          # "example.com"
{{ $json.title.includes('urgent') }}     # true/false
{{ $json.message.replace('foo','bar') }} # replace text
{{ $json.name.trim() }}                  # strip whitespace
{{ $json.code.padStart(6,'0') }}         # "000042"

# Template literals
{{ `Hello ${$json.name}, score: ${$json.score}` }}

# Conditional (ternary)
{{ $json.score >= 70 ? 'Pass' : 'Fail' }}

When expressions aren't enough, the Code node gives you a full JavaScript environment. Access all input items via $input.all() and return a new array of items.

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

const result = items.map(item => {
  const data = item.json;
  return {
    json: {
      fullName: `${data.firstName} ${data.lastName}`,
      emailDomain: data.email.split('@')[1],
      isHighValue: data.orderTotal > 1000,
      processedAt: new Date().toISOString()
    }
  };
});

return result;

// Filter: only keep items where score > 70
const items = $input.all();
return items
  .filter(item => item.json.score > 70)
  .map(item => ({ json: item.json }));

// Group items by category
const grouped = {};
$input.all().forEach(item => {
  const cat = item.json.category;
  if (!grouped[cat]) grouped[cat] = [];
  grouped[cat].push(item.json);
});
return Object.entries(grouped).map(([cat, rows]) => ({
  json: { category: cat, count: rows.length, items: rows }
}));

// Flatten a nested array from an API response
const raw = $input.first().json.data.users;
return raw.map(user => ({ json: user }));