JavaScript Fix TypeError: Cannot Set Properties of Undefined

The error Uncaught TypeError: Cannot set properties of undefined (setting ‘x’) happens when you try to set a property of an undefined value.

You probably mistake an undefined variable for an object. For example, suppose you have a variable named user as follows:

let user;

user.name = 'Nathan';

Here, we tried to set the property name of the user variable, but because the variable is never initialized, it has the value of undefined, and we get this error as a result:

TypeError: Cannot set properties of undefined (setting 'name')

To prevent this error, you need to make sure that you’re setting a property of an object and not an undefined value.

You can create an empty object using the curly brackets {} literal:

let user = {}; // ✅

user.name = 'Nathan';
user['age'] = 29;

console.log(user);

Because the user variable is now an empty object, you can set the name property of the variable just fine.

You can use both the dot . notation and the square brackets [] notation when setting the properties of an object.

And that’s how you fix the error. Hope this helps!