Got a warning: DOMNodeInserted & MutationObserver

[g8up]

Got a warning

[Violation] Added synchronous DOM mutation listener to a 'DOMNodeInserted' event. Consider using MutationObserver to make the page more responsive.
(anonymous) @ lookup.js:42

env

MacBook
Halo Word Dictionary v0.6.11
Chrome 版本 71.0.3578.80（正式版本） （64 位）