I am somewhat new to JS, and I've run into an error I am unable to resolve while using Intersection Observer.

Here is the code I am attempting to use:

const header = document.querySelector("navBarContainer");
const imageHeader = document.querySelector("myImageHeader");

const imageHeaderOptions = {
  rootMargin: "-50px 0px 0px 0px"
};

const imageHeaderObserver = new IntersectionObserver(function(
  entries,
  imageHeaderObserver
) {
  entries.forEach(entry => {
    if (!entry.isIntersecting) {
      header.classList.add("scrolled");
    } else {
      header.classList.remove("scrolled");
    }
  });
},
imageHeaderOptions);

imageHeaderObserver.observe(imageHeader);