n8n-expression-testing

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n8n Expression Testing

n8n 表达式测试

<default_to_action> When testing n8n expressions:

VALIDATE syntax before execution
TEST with multiple context scenarios
CHECK for null/undefined handling
VERIFY type safety
SCAN for security vulnerabilities

Quick Expression Checklist:

Valid JavaScript syntax
Context variables properly referenced ($json, $node)
Null-safe access patterns (?., ??)
No dangerous functions (eval, Function)
Efficient for large data sets

Common Pitfalls:

Accessing nested properties without null checks
Type coercion issues
Missing fallback values
Inefficient array operations </default_to_action>

<default_to_action> 测试n8n表达式时：

执行前验证语法
使用多上下文场景测试
检查空值/未定义值的处理
验证类型安全性
扫描安全漏洞

快速表达式检查清单：

有效的JavaScript语法
上下文变量引用正确（$json, $node）
空值安全访问模式（?. , ??）
无危险函数（eval, Function）
针对大数据集的高效处理

常见陷阱：

访问嵌套属性时未做空值检查
类型强制转换问题
缺少回退值
低效的数组操作 </default_to_action>

Quick Reference Card

快速参考卡片

n8n Expression Syntax

n8n 表达式语法

Pattern	Example	Description
Basic access	`{{ $json.field }}`	Access JSON field
Nested access	`{{ $json.user.email }}`	Access nested property
Array access	`{{ $json.items[0] }}`	Access array element
Node reference	`{{ $node["Name"].json.id }}`	Access other node's data
Method call	`{{ $json.name.toLowerCase() }}`	Call string method
Conditional	`{{ $json.x ? "yes" : "no" }}`	Ternary expression

模式	示例	说明
基础访问	`{{ $json.field }}`	访问JSON字段
嵌套访问	`{{ $json.user.email }}`	访问嵌套属性
数组访问	`{{ $json.items[0] }}`	访问数组元素
节点引用	`{{ $node["Name"].json.id }}`	访问其他节点的数据
方法调用	`{{ $json.name.toLowerCase() }}`	调用字符串方法
条件表达式	`{{ $json.x ? "yes" : "no" }}`	三元表达式

Context Variables

上下文变量

Variable	Description	Example
`$json`	Current item data	`{{ $json.email }}`
`$node["Name"]`	Other node's data	`{{ $node["HTTP"].json.body }}`
`$items()`	Multiple items	`{{ $items("Node", 0, 0).json }}`
`$now`	Current timestamp	`{{ $now.toISO() }}`
`$today`	Today's date	`{{ $today }}`
`$runIndex`	Run iteration	`{{ $runIndex }}`
`$workflow`	Workflow info	`{{ $workflow.name }}`

变量	说明	示例
`$json`	当前项数据	`{{ $json.email }}`
`$node["Name"]`	其他节点的数据	`{{ $node["HTTP"].json.body }}`
`$items()`	多个项数据	`{{ $items("Node", 0, 0).json }}`
`$now`	当前时间戳	`{{ $now.toISO() }}`
`$today`	今日日期	`{{ $today }}`
`$runIndex`	运行迭代次数	`{{ $runIndex }}`
`$workflow`	工作流信息	`{{ $workflow.name }}`

Expression Syntax Patterns

表达式语法模式

Safe Data Access

安全数据访问

javascript

// BAD: Can fail if nested objects are null
{{ $json.user.profile.email }}

// GOOD: Optional chaining with fallback
{{ $json.user?.profile?.email ?? '' }}

// BAD: Array access without bounds check
{{ $json.items[0].name }}

// GOOD: Safe array access
{{ $json.items?.[0]?.name ?? 'No items' }}

javascript

// BAD: Can fail if nested objects are null
{{ $json.user.profile.email }}

// GOOD: Optional chaining with fallback
{{ $json.user?.profile?.email ?? '' }}

// BAD: Array access without bounds check
{{ $json.items[0].name }}

// GOOD: Safe array access
{{ $json.items?.[0]?.name ?? 'No items' }}

Type Conversions

类型转换

javascript

// String to Number
{{ parseInt($json.quantity, 10) }}
{{ parseFloat($json.price) }}
{{ Number($json.value) }}

// Number to String
{{ String($json.id) }}
{{ $json.amount.toString() }}
{{ $json.count.toFixed(2) }}

// Date handling
{{ new Date($json.timestamp).toISOString() }}
{{ DateTime.fromISO($json.date).toFormat('yyyy-MM-dd') }}

// Boolean conversion
{{ Boolean($json.active) }}
{{ $json.enabled === 'true' }}

javascript

// String to Number
{{ parseInt($json.quantity, 10) }}
{{ parseFloat($json.price) }}
{{ Number($json.value) }}

// Number to String
{{ String($json.id) }}
{{ $json.amount.toString() }}
{{ $json.count.toFixed(2) }}

// Date handling
{{ new Date($json.timestamp).toISOString() }}
{{ DateTime.fromISO($json.date).toFormat('yyyy-MM-dd') }}

// Boolean conversion
{{ Boolean($json.active) }}
{{ $json.enabled === 'true' }}

String Operations

字符串操作

javascript

// Case conversion
{{ $json.name.toLowerCase() }}
{{ $json.name.toUpperCase() }}
{{ $json.name.charAt(0).toUpperCase() + $json.name.slice(1) }}

// String manipulation
{{ $json.text.trim() }}
{{ $json.text.replace(/\s+/g, ' ') }}
{{ $json.text.substring(0, 100) }}

// Template strings
{{ `Hello, ${$json.firstName} ${$json.lastName}!` }}
{{ `Order #${$json.orderId} - ${$json.status}` }}

javascript

// Case conversion
{{ $json.name.toLowerCase() }}
{{ $json.name.toUpperCase() }}
{{ $json.name.charAt(0).toUpperCase() + $json.name.slice(1) }}

// String manipulation
{{ $json.text.trim() }}
{{ $json.text.replace(/\s+/g, ' ') }}
{{ $json.text.substring(0, 100) }}

// Template strings
{{ `Hello, ${$json.firstName} ${$json.lastName}!` }}
{{ `Order #${$json.orderId} - ${$json.status}` }}

Array Operations

数组操作

javascript

// Mapping
{{ $json.items.map(item => item.name) }}
{{ $json.items.map(item => ({ id: item.id, total: item.price * item.qty })) }}

// Filtering
{{ $json.items.filter(item => item.active) }}
{{ $json.items.filter(item => item.price > 100) }}

// Reducing
{{ $json.items.reduce((sum, item) => sum + item.price, 0) }}
{{ $json.items.reduce((acc, item) => ({ ...acc, [item.id]: item }), {}) }}

// Finding
{{ $json.items.find(item => item.id === $json.targetId) }}
{{ $json.items.findIndex(item => item.name === 'target') }}

// Joining
{{ $json.tags.join(', ') }}
{{ $json.items.map(i => i.name).join(' | ') }}

javascript

// Mapping
{{ $json.items.map(item => item.name) }}
{{ $json.items.map(item => ({ id: item.id, total: item.price * item.qty })) }}

// Filtering
{{ $json.items.filter(item => item.active) }}
{{ $json.items.filter(item => item.price > 100) }}

// Reducing
{{ $json.items.reduce((sum, item) => sum + item.price, 0) }}
{{ $json.items.reduce((acc, item) => ({ ...acc, [item.id]: item }), {}) }}

// Finding
{{ $json.items.find(item => item.id === $json.targetId) }}
{{ $json.items.findIndex(item => item.name === 'target') }}

// Joining
{{ $json.tags.join(', ') }}
{{ $json.items.map(i => i.name).join(' | ') }}

Validation Patterns

验证模式

typescript

// Validate expression syntax
function validateExpressionSyntax(expression: string): ValidationResult {
  // Remove n8n template markers
  const code = expression.replace(/\{\{|\}\}/g, '').trim();

  try {
    // Check if valid JavaScript
    new Function(`return (${code})`);
    return { valid: true };
  } catch (error) {
    return {
      valid: false,
      error: error.message,
      suggestion: suggestFix(error.message, code)
    };
  }
}

// Validate context variables
function validateContextVariables(expression: string): string[] {
  const contextVars = ['$json', '$node', '$items', '$now', '$today', '$runIndex', '$workflow'];
  const usedVars = [];
  const invalidVars = [];

  // Find all $ prefixed variables
  const varPattern = /\$\w+/g;
  let match;

  while ((match = varPattern.exec(expression)) !== null) {
    const varName = match[0];
    if (contextVars.some(cv => varName.startsWith(cv))) {
      usedVars.push(varName);
    } else {
      invalidVars.push(varName);
    }
  }

  return { usedVars, invalidVars };
}

// Test expression with sample data
function testExpression(expression: string, context: any): TestResult {
  const code = expression.replace(/\{\{|\}\}/g, '').trim();

  try {
    // Create function with context
    const fn = new Function('$json', '$node', '$items', '$now', '$today',
      `return (${code})`);

    const result = fn(
      context.$json || {},
      context.$node || {},
      context.$items || (() => ({})),
      context.$now || new Date(),
      context.$today || new Date()
    );

    return { success: true, result };
  } catch (error) {
    return { success: false, error: error.message };
  }
}

typescript

// Validate expression syntax
function validateExpressionSyntax(expression: string): ValidationResult {
  // Remove n8n template markers
  const code = expression.replace(/\{\{|\}\}/g, '').trim();

  try {
    // Check if valid JavaScript
    new Function(`return (${code})`);
    return { valid: true };
  } catch (error) {
    return {
      valid: false,
      error: error.message,
      suggestion: suggestFix(error.message, code)
    };
  }
}

// Validate context variables
function validateContextVariables(expression: string): string[] {
  const contextVars = ['$json', '$node', '$items', '$now', '$today', '$runIndex', '$workflow'];
  const usedVars = [];
  const invalidVars = [];

  // Find all $ prefixed variables
  const varPattern = /\$\w+/g;
  let match;

  while ((match = varPattern.exec(expression)) !== null) {
    const varName = match[0];
    if (contextVars.some(cv => varName.startsWith(cv))) {
      usedVars.push(varName);
    } else {
      invalidVars.push(varName);
    }
  }

  return { usedVars, invalidVars };
}

// Test expression with sample data
function testExpression(expression: string, context: any): TestResult {
  const code = expression.replace(/\{\{|\}\}/g, '').trim();

  try {
    // Create function with context
    const fn = new Function('$json', '$node', '$items', '$now', '$today',
      `return (${code})`);

    const result = fn(
      context.$json || {},
      context.$node || {},
      context.$items || (() => ({})),
      context.$now || new Date(),
      context.$today || new Date()
    );

    return { success: true, result };
  } catch (error) {
    return { success: false, error: error.message };
  }
}

Common Errors and Fixes

常见错误与修复

Undefined Property Access

未定义属性访问

javascript

// ERROR: Cannot read property 'email' of undefined
{{ $json.user.email }}

// FIX 1: Optional chaining
{{ $json.user?.email }}

// FIX 2: With fallback
{{ $json.user?.email ?? 'no-email@example.com' }}

// FIX 3: Conditional
{{ $json.user ? $json.user.email : '' }}

javascript

// ERROR: Cannot read property 'email' of undefined
{{ $json.user.email }}

// FIX 1: Optional chaining
{{ $json.user?.email }}

// FIX 2: With fallback
{{ $json.user?.email ?? 'no-email@example.com' }}

// FIX 3: Conditional
{{ $json.user ? $json.user.email : '' }}

Type Errors

类型错误

javascript

// ERROR: toLowerCase is not a function (when null)
{{ $json.name.toLowerCase() }}

// FIX: Null check first
{{ $json.name?.toLowerCase() ?? '' }}

// ERROR: toFixed is not a function (string instead of number)
{{ $json.price.toFixed(2) }}

// FIX: Parse as number first
{{ parseFloat($json.price).toFixed(2) }}

// ERROR: map is not a function (not an array)
{{ $json.items.map(i => i.name) }}

// FIX: Ensure array
{{ (Array.isArray($json.items) ? $json.items : []).map(i => i.name) }}

javascript

// ERROR: toLowerCase is not a function (when null)
{{ $json.name.toLowerCase() }}

// FIX: Null check first
{{ $json.name?.toLowerCase() ?? '' }}

// ERROR: toFixed is not a function (string instead of number)
{{ $json.price.toFixed(2) }}

// FIX: Parse as number first
{{ parseFloat($json.price).toFixed(2) }}

// ERROR: map is not a function (not an array)
{{ $json.items.map(i => i.name) }}

// FIX: Ensure array
{{ (Array.isArray($json.items) ? $json.items : []).map(i => i.name) }}

Node Reference Errors

节点引用错误

javascript

// ERROR: Node "Previous Node" not found
{{ $node["Previous Node"].json.data }}

// FIX: Use exact node name (case-sensitive)
{{ $node["Previous Node1"].json.data }}

// FIX: Add fallback for safety
{{ $node["Previous Node"]?.json?.data ?? {} }}

javascript

// ERROR: Node "Previous Node" not found
{{ $node["Previous Node"].json.data }}

// FIX: Use exact node name (case-sensitive)
{{ $node["Previous Node1"].json.data }}

// FIX: Add fallback for safety
{{ $node["Previous Node"]?.json?.data ?? {} }}

Security Patterns

安全模式

Dangerous Functions to Avoid

需避免的危险函数

javascript

// DANGEROUS: Never use eval
{{ eval($json.code) }}

// DANGEROUS: Dynamic function creation
{{ new Function($json.code)() }}

// DANGEROUS: setTimeout with string
{{ setTimeout($json.code, 1000) }}

// SAFE: Use explicit operations instead
{{ $json.value * 2 }}
{{ JSON.parse($json.jsonString) }}

javascript

// DANGEROUS: Never use eval
{{ eval($json.code) }}

// DANGEROUS: Dynamic function creation
{{ new Function($json.code)() }}

// DANGEROUS: setTimeout with string
{{ setTimeout($json.code, 1000) }}

// SAFE: Use explicit operations instead
{{ $json.value * 2 }}
{{ JSON.parse($json.jsonString) }}

Input Validation

输入验证

javascript

// Validate email format
{{ /^[^\s@]+@[^\s@]+\.[^\s@]+$/.test($json.email) ? $json.email : '' }}

// Sanitize for HTML (basic)
{{ $json.text.replace(/[<>&"']/g, c => ({
  '<': '&lt;', '>': '&gt;', '&': '&amp;', '"': '&quot;', "'": '&#39;'
}[c])) }}

// Limit string length
{{ $json.input.substring(0, 1000) }}

// Validate number range
{{ Math.min(Math.max(parseInt($json.value), 0), 100) }}

javascript

// Validate email format
{{ /^[^\s@]+@[^\s@]+\.[^\s@]+$/.test($json.email) ? $json.email : '' }}

// Sanitize for HTML (basic)
{{ $json.text.replace(/[<>&"']/g, c => ({
  '<': '&lt;', '>': '&gt;', '&': '&amp;', '"': '&quot;', "'": '&#39;'
}[c])) }}

// Limit string length
{{ $json.input.substring(0, 1000) }}

// Validate number range
{{ Math.min(Math.max(parseInt($json.value), 0), 100) }}

Performance Optimization

性能优化

Efficient Array Operations

高效数组操作

javascript

// SLOW: Multiple iterations
{{ $json.items.filter(i => i.active).map(i => i.name).join(', ') }}

// FASTER: Single reduce
{{ $json.items.reduce((acc, i) => i.active ? (acc ? `${acc}, ${i.name}` : i.name) : acc, '') }}

// SLOW: Nested loops
{{ $json.items.map(i => $json.categories.find(c => c.id === i.categoryId)) }}

// FASTER: Create lookup map first (in Code node)
const categoryMap = Object.fromEntries($json.categories.map(c => [c.id, c]));
return $json.items.map(i => categoryMap[i.categoryId]);

javascript

// SLOW: Multiple iterations
{{ $json.items.filter(i => i.active).map(i => i.name).join(', ') }}

// FASTER: Single reduce
{{ $json.items.reduce((acc, i) => i.active ? (acc ? `${acc}, ${i.name}` : i.name) : acc, '') }}

// SLOW: Nested loops
{{ $json.items.map(i => $json.categories.find(c => c.id === i.categoryId)) }}

// FASTER: Create lookup map first (in Code node)
const categoryMap = Object.fromEntries($json.categories.map(c => [c.id, c]));
return $json.items.map(i => categoryMap[i.categoryId]);

Avoid in Expressions

表达式中需避免的操作

javascript

// AVOID: Complex logic in expressions
{{ $json.items.reduce((acc, item) => {
  const category = $json.categories.find(c => c.id === item.catId);
  if (category && category.active) {
    acc.push({ ...item, categoryName: category.name });
  }
  return acc;
}, []) }}

// BETTER: Move to Code node for complex transformations

javascript

// AVOID: Complex logic in expressions
{{ $json.items.reduce((acc, item) => {
  const category = $json.categories.find(c => c.id === item.catId);
  if (category && category.active) {
    acc.push({ ...item, categoryName: category.name });
  }
  return acc;
}, []) }}

// BETTER: Move to Code node for complex transformations

Testing Patterns

测试模式

typescript

// Expression test suite
const expressionTests = [
  {
    name: 'Basic property access',
    expression: '{{ $json.name }}',
    context: { $json: { name: 'John' } },
    expected: 'John'
  },
  {
    name: 'Nested with optional chaining',
    expression: '{{ $json.user?.email ?? "default" }}',
    context: { $json: { user: null } },
    expected: 'default'
  },
  {
    name: 'Array mapping',
    expression: '{{ $json.items.map(i => i.id).join(",") }}',
    context: { $json: { items: [{ id: 1 }, { id: 2 }] } },
    expected: '1,2'
  },
  {
    name: 'Conditional expression',
    expression: '{{ $json.score >= 70 ? "Pass" : "Fail" }}',
    context: { $json: { score: 85 } },
    expected: 'Pass'
  },
  {
    name: 'Node reference',
    expression: '{{ $node["Previous"].json.result }}',
    context: { $node: { Previous: { json: { result: 'success' } } } },
    expected: 'success'
  }
];

// Run tests
for (const test of expressionTests) {
  const result = testExpression(test.expression, test.context);
  console.log(`${test.name}: ${result.result === test.expected ? 'PASS' : 'FAIL'}`);
}

typescript

// Expression test suite
const expressionTests = [
  {
    name: 'Basic property access',
    expression: '{{ $json.name }}',
    context: { $json: { name: 'John' } },
    expected: 'John'
  },
  {
    name: 'Nested with optional chaining',
    expression: '{{ $json.user?.email ?? "default" }}',
    context: { $json: { user: null } },
    expected: 'default'
  },
  {
    name: 'Array mapping',
    expression: '{{ $json.items.map(i => i.id).join(",") }}',
    context: { $json: { items: [{ id: 1 }, { id: 2 }] } },
    expected: '1,2'
  },
  {
    name: 'Conditional expression',
    expression: '{{ $json.score >= 70 ? "Pass" : "Fail" }}',
    context: { $json: { score: 85 } },
    expected: 'Pass'
  },
  {
    name: 'Node reference',
    expression: '{{ $node["Previous"].json.result }}',
    context: { $node: { Previous: { json: { result: 'success' } } } },
    expected: 'success'
  }
];

// Run tests
for (const test of expressionTests) {
  const result = testExpression(test.expression, test.context);
  console.log(`${test.name}: ${result.result === test.expected ? 'PASS' : 'FAIL'}`);
}

Agent Coordination

Agent 协作

Memory Namespace

命名空间内存

aqe/n8n/expressions/
├── validations/*    - Expression validation results
├── patterns/*       - Discovered expression patterns
├── errors/*         - Common error catalog
└── optimizations/*  - Performance suggestions

aqe/n8n/expressions/
├── validations/*    - Expression validation results
├── patterns/*       - Discovered expression patterns
├── errors/*         - Common error catalog
└── optimizations/*  - Performance suggestions

Fleet Coordination

集群协作

typescript

// Coordinate expression validation with workflow testing
await Task("Validate expressions", {
  workflowId: "wf-123",
  validateAll: true,
  testWithSampleData: true
}, "n8n-expression-validator");

typescript

// Coordinate expression validation with workflow testing
await Task("Validate expressions", {
  workflowId: "wf-123",
  validateAll: true,
  testWithSampleData: true
}, "n8n-expression-validator");

Related Skills

Remember

注意事项

n8n expressions are JavaScript-like with special context variables ($json, $node, etc.). Testing requires:

Syntax validation
Context variable verification
Null safety checks
Type compatibility
Security scanning

Key patterns: Use optional chaining (

?.

) and nullish coalescing (

??

) for safety. Move complex logic to Code nodes. Always test with edge cases (null, undefined, empty arrays).

n8n 表达式类JavaScript语法，包含特殊上下文变量（$json、$node等）。测试时需注意：

语法验证
上下文变量校验
空值安全检查
类型兼容性
安全扫描

核心模式： 使用可选链（

?.

）和空值合并运算符（

??

）保障安全。将复杂逻辑转移至Code节点。始终使用边缘案例（空值、未定义值、空数组）进行测试。

n8n-expression-testing

Original

Translation

n8n Expression Testing

n8n 表达式测试

Quick Reference Card

快速参考卡片

n8n Expression Syntax

n8n 表达式语法

Context Variables

上下文变量

Expression Syntax Patterns

表达式语法模式

Safe Data Access

安全数据访问

Type Conversions

类型转换

String Operations

字符串操作

Array Operations

数组操作

Validation Patterns

验证模式

Common Errors and Fixes

常见错误与修复

Undefined Property Access

未定义属性访问

Type Errors

类型错误

Node Reference Errors

节点引用错误

Security Patterns

安全模式

Dangerous Functions to Avoid

需避免的危险函数

Input Validation

输入验证

Performance Optimization

性能优化

Efficient Array Operations

高效数组操作

Avoid in Expressions

表达式中需避免的操作

Testing Patterns

测试模式

Agent Coordination

Agent 协作

Memory Namespace

命名空间内存

Fleet Coordination

集群协作

Related Skills

相关技能

Remember

注意事项