Echo JS 0.11.0

> We have found that using insertAdjacentHTML() rather than .innerHTML() appends the HTML rather than replacing the current content.

? What does that even mean? It's not that you've found a new species of ants in the rain forest: insertAdjacentHTML is a well-known method from IE6 (IIRC the version) that's been adopted as a standard in recent times.
(It also needs two arguments - the first one being a positional string like 'beforeEnd'.)
(And innerHTML isn't a method, so don't add parentheses after it.)