Function must have JSDoc.
export function log() {
^^^^^^^^^^^^^^^^
import statements are not sorted.
channel.port1.onmessage = e => {
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Bad type annotation. expected closing } See https://github.com/google/closure-compiler/wiki/Bad-Type-Annotation for more information.
* @param {!Function():boolean} isViewerHidden method that determines if viewer is hidden.
import statements are not sorted.
Extra @return clauses in the JsDoc