It means you’ve tried to insert a DOM node into a place in the DOM tree where it cannot go. The most common place I see this is on Safari which doesn’t allow the following:
document.appendChild(document.createElement('div'));
Generally, this is just a mistake where this was actually intended:
document.body.appendChild(document.createElement('div'));
Other causes seen in the wild (summarized from comments):
- You are attempting to append a node to itself
- You are attempting to append null to a node
- You are attempting to append a node to a text node.
- Your HTML is invalid (e.g. failing to close your target node)
- The browser thinks the HTML you are attempting to append is XML (fix by adding
<!doctype html>
to your injected HTML, or specifying the content type when fetching via XHR)