Expressions & Variables

Expressions là "ngôn ngữ" bên trong n8n — cho phép bạn truy cập data từ nodes, transform values, và build dynamic logic.

🎯 Mục tiêu bài học

TB5 min

🎯 Mục tiêu

Hiểu n8n expression syntax
Truy cập data từ current và previous nodes
Sử dụng built-in variables
String, date, và number operations

Checkpoint

Expressions trong n8n là gì? Tại sao chúng quan trọng cho dynamic workflows?

Task 0

📖 Expression Basics

TB5 min

1. Expression Basics

1.1 Syntax

Ví dụ

1{{ expression }}
2 
3Ví dụ:
4{{ $json.name }}              → Truy cập field "name" của current item
5{{ $json.user.email }}        → Nested field
6{{ $json.items[0].price }}    → Array element
7{{ "Hello " + $json.name }}   → String concatenation

1.2 Khi nào dùng Expression?

Mọi field trong n8n node đều có thể dùng expression (icon fx):

Ví dụ

1✅ Dynamic values: {{ $json.email }}
2✅ Calculations: {{ $json.price * 1.1 }}
3✅ Conditions: {{ $json.age >= 18 ? "Adult" : "Minor" }}
4✅ Templates: {{ "Dear " + $json.name + "," }}
5✅ Date formatting: {{ $now.format('yyyy-MM-dd') }}

Checkpoint

Cú pháp expression trong n8n là gì? Cho 3 ví dụ common expressions.

Task 1

📊 Accessing Data

TB5 min

2. Accessing Data

2.1 Current Node Data

Ví dụ

1{{ $json }}           → Toàn bộ JSON object của current item
2{{ $json.name }}      → Field "name"
3{{ $json.address.city }}  → Nested object
4{{ $json.tags[0] }}   → First element of array
5{{ $json.tags.length }}   → Array length

2.2 Previous Node Data

Ví dụ

1{{ $('Node Name').item.json.fieldName }}
2 
3Ví dụ:
4{{ $('Google Sheets').item.json.email }}
5{{ $('HTTP Request').item.json.data.total }}
6{{ $('Webhook').item.json.body.name }}

2.3 All Items from Previous Node

Ví dụ

1{{ $('Node Name').all() }}           → All items as array
2{{ $('Node Name').all().length }}    → Number of items
3{{ $('Node Name').first().json }}    → First item
4{{ $('Node Name').last().json }}     → Last item

2.4 Multiple Items

Ví dụ

1// Khi node trả về nhiều items
2{{ $json }}                  → Current item trong loop
3{{ $itemIndex }}             → Index of current item (0-based)
4{{ $('Node').all()[2].json }} → Specific item by index

Checkpoint

Phân biệt $json, $('Node Name').item.json, và $('Node').all(). Khi nào dùng cái nào?

Task 2

🔧 Built-in Variables

TB5 min

3. Built-in Variables

3.1 Execution Variables

Variable	Description	Example
`$now`	Current datetime	`2026-01-20T09:30:00`
`$today`	Today's date	`2026-01-20`
`$itemIndex`	Current item index	`0, 1, 2...`
`$runIndex`	Execution run number	`0`
`$workflow`	Workflow metadata	`$workflow.name`
`$execution`	Execution metadata	`$execution.id`
`$env`	Environment variables	`$env.API_KEY`

3.2 Date/Time

Ví dụ

1{{ $now }}                            → 2026-01-20T09:30:00.000+07:00
2{{ $now.format('yyyy-MM-dd') }}       → 2026-01-20
3{{ $now.format('HH:mm') }}           → 09:30
4{{ $now.format('dd/MM/yyyy') }}      → 20/01/2026
5{{ $now.minus(1, 'day') }}           → Yesterday
6{{ $now.plus(7, 'days') }}           → Next week
7{{ $now.startOf('month') }}          → 2026-01-01
8{{ $now.endOf('month') }}            → 2026-01-31
9{{ $today.weekday }}                 → 1 (Monday)

3.3 Environment Variables

Ví dụ

1Setup: n8n Settings → Variables
2  API_KEY = "xxxxx"
3  ENVIRONMENT = "production"
4 
5Access: {{ $env.API_KEY }}

Checkpoint

Kể ra 5 built-in variables trong n8n và cho ví dụ sử dụng cho mỗi biến.

Task 3

✂️ String Operations

TB5 min

4. String Operations

4.1 Basic String Methods

Ví dụ

1{{ $json.name.toUpperCase() }}          → "NGUYEN VAN A"
2{{ $json.name.toLowerCase() }}          → "nguyen van a"
3{{ $json.email.trim() }}                → Remove whitespace
4{{ $json.text.slice(0, 100) }}          → First 100 characters
5{{ $json.name.replace('old', 'new') }}  → Replace text
6{{ $json.text.includes('keyword') }}    → true/false
7{{ $json.text.split(',') }}             → Array from CSV
8{{ $json.parts.join(', ') }}            → Array to string

4.2 Template Strings

Ví dụ

1{{ `Dear ${$json.name},
2 
3Your order #${$json.orderId} has been shipped.
4Estimated delivery: ${$json.deliveryDate}.
5 
6Thank you!` }}

4.3 Conditional Text

Ví dụ

1{{ $json.status === 'active' ? '🟢 Active' : '🔴 Inactive' }}
2 
3{{ $json.score >= 90 ? 'Excellent' 
4   : $json.score >= 70 ? 'Good' 
5   : 'Needs improvement' }}

Checkpoint

Viết expression template string gửi email personalized với tên và orderId của khách hàng.

Task 4

🔢 Number Operations

TB5 min

5. Number Operations

5.1 Math

Ví dụ

1{{ $json.price * 1.1 }}              → +10% tax
2{{ $json.price * 0.8 }}              → 20% discount
3{{ Math.round($json.value) }}        → Round
4{{ Math.floor($json.value) }}        → Round down
5{{ Math.ceil($json.value) }}         → Round up
6{{ $json.total.toFixed(2) }}         → "123.45" (2 decimals)
7{{ Math.max($json.a, $json.b) }}     → Larger value
8{{ Math.min($json.a, $json.b) }}     → Smaller value

5.2 Aggregations

Ví dụ

1// Sum all items' price
2{{ $('Node').all().reduce((sum, item) => sum + item.json.price, 0) }}
3 
4// Average
5{{ $('Node').all().reduce((sum, item) => sum + item.json.score, 0) / $('Node').all().length }}
6 
7// Count with condition
8{{ $('Node').all().filter(item => item.json.status === 'active').length }}

5.3 Currency Formatting

Ví dụ

1{{ new Intl.NumberFormat('vi-VN', { style: 'currency', currency: 'VND' }).format($json.amount) }}
2→ "1.500.000 ₫"
3 
4{{ new Intl.NumberFormat('en-US', { style: 'currency', currency: 'USD' }).format($json.amount) }}
5→ "$1,500.00"

Checkpoint

Viết expression tính tổng giá trị (sum) của tất cả items từ node trước. Dùng method nào?

Task 5

📦 Object & Array Operations

TB5 min

6. Object & Array Operations

6.1 Object Access

Ví dụ

1{{ Object.keys($json) }}              → ["name", "email", "age"]
2{{ Object.values($json.scores) }}     → [85, 92, 78]
3{{ Object.entries($json).length }}    → Number of fields
4{{ JSON.stringify($json) }}           → Convert to string
5{{ JSON.parse($json.jsonString) }}    → Parse string to object

6.2 Array Operations

Ví dụ

1{{ $json.items.map(i => i.name) }}                    → Extract names
2{{ $json.items.filter(i => i.price > 100) }}          → Filter
3{{ $json.items.find(i => i.id === 123) }}             → Find one
4{{ $json.items.sort((a, b) => a.price - b.price) }}   → Sort
5{{ $json.items.some(i => i.stock === 0) }}            → Any out of stock?
6{{ $json.items.every(i => i.price > 0) }}             → All have price?
7{{ [...new Set($json.categories)] }}                  → Unique values

6.3 Spread & Merge

Ví dụ

1// Merge objects
2{{ { ...$json, status: 'processed', processedAt: $now } }}
3 
4// Flatten nested array
5{{ $json.orders.flatMap(o => o.items) }}

Checkpoint

Array method nào dùng để lọc items? Cho ví dụ filter items có price > 100.

Task 6

🔁 Common Expression Patterns

TB5 min

7. Common Expression Patterns

7.1 Default Values

Ví dụ

1{{ $json.name || 'Unknown' }}           → Fallback if null/empty
2{{ $json.phone ?? 'N/A' }}              → Nullish coalescing

7.2 Data Cleaning

Ví dụ

1// Remove extra spaces
2{{ $json.name.trim().replace(/\s+/g, ' ') }}
3 
4// Extract email domain
5{{ $json.email.split('@')[1] }}
6 
7// Capitalize first letter
8{{ $json.name.charAt(0).toUpperCase() + $json.name.slice(1) }}

7.3 URL Building

Ví dụ

1{{ `https://api.example.com/users/${$json.userId}/orders?status=${$json.status}&page=${$json.page}` }}

7.4 Conditional Logic

Ví dụ

1// Multiple conditions
2{{ 
3  $json.type === 'urgent' && $json.amount > 1000000
4    ? '#critical-alerts'
5    : $json.type === 'urgent'
6    ? '#alerts'
7    : '#general'
8}}

8. Hands-on Lab

Lab 1: Data Formatting Pipeline

Build workflow:

Google Sheets — Get raw data (names, emails, dates, amounts)
Set node — Transform using expressions:
- Name: Title case
- Email: lowercase, trim
- Amount: VND format
- Date: dd/MM/yyyy format
Slack — Post formatted summary

Lab 2: Dynamic Email Template

Airtable — Get customer data
Set node — Build email subject & body using expressions:
- Greet by name
- Show order details
- Calculate total with tax
- Conditional urgency message
Email — Send personalized email

Lab 3: Report Generator

HTTP Request — Get sales data API
Expressions — Calculate:
- Total revenue (sum)
- Average order value
- Top product (max)
- MoM growth %
Slack — Post report with emoji indicators

📝 Quiz

🎯 Key Takeaways

{{ }} — Expression syntax trong mọi n8n field
$json — Current item data
$('Node') — Access previous node data
$now — Current datetime với format methods
JavaScript — Full JS support (strings, arrays, objects, math)

Checkpoint

Viết expression chọn Slack channel dựa trên type và amount của item (dùng conditional logic).

Task 7

🚀 Bài tiếp theo

Data Transformation — Set, Merge, Split, Filter, và Sort nodes!