🔍 How to Fix JavaScript Uncaught TypeError: Cannot Read Property of Undefined

One of the most common JavaScript errors developers face is: "Uncaught TypeError: Cannot read property of undefined". This post explains the cause, shows an example, and provides a step-by-step solution.

💡 What Does This Error Mean?

This error occurs when you're trying to access a property of a variable that is undefined. For example:

let user;
console.log(user.name); // ❌ Uncaught TypeError: Cannot read property 'name' of undefined

🛠️ Step-by-Step Solution

1. Step 1: Check if the variable is defined before accessing properties.
2. Step 2: Use optional chaining ?. (ES11+) for safe access.
3. Step 3: Set default values using || or ??.

✅ Corrected & Runnable Code

Here’s the safe version using all best practices:

let user = undefined;

// ✅ Safe access using optional chaining
console.log(user?.name || "Name not found");

// ✅ Using default object
user = user || { name: "Guest" };
console.log("Welcome, " + user.name);

🧪 Try It Yourself

📌 Final Thoughts

By understanding and avoiding the "Cannot read property of undefined" error in JavaScript, you can make your code more robust and prevent unexpected runtime crashes.

🗨️ Have questions? Leave a comment below or share this with your fellow developers!