Uncaught TypeError: Cannot read properties of undefined (reading 'toString')

Question

I am developing a React app and I don't know how to solve this error. I'm pretty sure it's from my useEffect function, but I can't figure out what's wrong. Any help would be much appreciated, thank you!

const CourseTypeFour = ({ data, classes, bgWhite }) => {
   let { id } = data;
   const [courseObject, setCourseObject] = useState({});

   useEffect(() => {
        axios.get(`http://localhost:3001/courses/${id}`).then((response) => {
          setCourseObject(response.data);
        });
    },[id]);

   return (
      ...
   )
}
export default CourseTypeFour;

Answer 1

The problem isn't in this part of the code. In error, you can see that problem is when you try to use the toString method on a variable that is undefined. Try to find part of the code where you use the toString method, and before it execute the console.log function with this variable to see what is inside.