TypeError: Cannot read properties of undefined

Why this happens

• The object was never assigned or was set to undefined

• A function returned undefined and the caller accessed a property on the result

• An array element or nested property is undefined (e.g., user.address.city when address is undefined)

Minimal example

let user;
console.log(user.name);

let user;
console.log(user?.name);

How to diagnose

• Log the object right before the property access to confirm it is undefined

• Trace where the object should have been assigned or returned

• Check API responses for missing fields that lead to undefined

How to fix

• Add a guard check before accessing the property (if (obj))

• Use optional chaining (obj?.property) to safely access nested properties

• Provide a default object so the property always exists

How to prevent

• Use optional chaining (?.) for all uncertain property accesses

• Validate API responses before using them

Related Resources