How to Fix n8n Expression Is Not Valid ⚠️ Cannot Read Properties of Undefined Error

Описание: Seeing “Expression is not valid: Cannot read properties of undefined” in n8n? 😩 This happens when your expression references a property or node output that doesn’t exist yet or has null/undefined values. In this tutorial, I’ll show you how to fix n8n expression errors by validating node outputs, using optional chaining, and handling undefined data safely.

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✅ What You’ll Learn / Fix:
⚠️ Why n8n throws “Cannot read properties of undefined”
🔧 How to check node outputs and ensure proper references
⚙️ Use optional chaining (?.) or fallback values in expressions
💡 Bonus: Debug expressions using Function nodes and logs

✅ Timestamps:
⏱️ 0:00 Intro
⚠️ 0:25 Why “Cannot read properties of undefined” occurs
🔧 1:00 Validate node outputs and data availability
⚙️ 1:45 Fix expressions with optional chaining or defaults
💡 2:20 Bonus – test and debug expressions safely
✅ 3:00 Wrap-up

✅ Why Watch This Video:
🔧 Fix n8n expression errors that break workflows
🚀 Prevent runtime crashes due to undefined data
💡 Learn best practices for writing safe and resilient expressions

✅ Who This Helps:
💻 n8n users working with dynamic data and expressions
⚙️ Developers debugging workflows with multiple node outputs
📱 Anyone automating tasks using Function or Set nodes in n8n

👍 Found This Helpful?
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💬 Comment if this fixed your undefined property error
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#n8n #ExpressionError #CannotReadProperties #Undefined #n8nTutorial #Automation #WorkflowFix #TechTips #DevOps #FunctionNode #DataValidation #WorkflowAutomation