How to fix TypeError: Cannot convert undefined or null to object in JavaScript

One error you might encounter when running JavaScript code is:

TypeError: Cannot convert undefined or null to object

This error occurs when you pass either null or undefined to a function that expects an object.

Usually, it happens when you call the Object methods like Object.keys(), Object.values(), and Object.assign().

Let’s see an example that causes this error and how you can fix it.

How to reproduce the error

To cause this error, you need to pass null or undefined to a function that requires an object.

The following example all cause the same error:

Object.keys(null);

Object.values(undefined);

Object.assign(null, {});

The above methods expected an object as its parameter, but both null and undefined can’t be converted into an object. Hence the error.

How to fix this error

To resolve this error, you need to make sure that you’re not passing null or undefined to the methods.

Most likely you’re passing a variable to the above methods. One way to check if the variable is null or undefined is to use an if statement as follows:

let myObj = {
  name: "John",
};

if (myObj) {
  // call the method here
  Object.assign(myObj, { age: 25 }); // ✅
}

console.log(myObj); // { name: 'John', age: 25 }

The error doesn’t appear when you run the code above because the if statement checks that the myObj variable is not null or undefined before calling the Object.assign() method.

You can also use a ternary operator and choose to call the method to replace the if statement as follows:

let myObj = undefined;

let newObj = myObj ? Object.assign(myObj, { age: 25 }) : {};

console.log(newObj); // {}

Because myObj is undefined, the Object.assign() method didn’t get called and the empty object is assigned to the newObj variable.

Another way to fix this error is to provide a fallback value when you define the argument to the method.

You can use the logical OR || operator and add a fallback value as follows:

let myObj = {
  name: "John",
};

const objKeys = Object.keys(myObj || {});

Here, an empty object {} serves as the fallback value when the value of myObj variable is null or undefined.

And that’s how you fix the TypeError: Cannot convert undefined or null to object in JavaScript.

I hope this tutorial helps. See you in other tutorials! 👋