Follow-up from "Performance Improvements to Vue MR page"

The following discussions from gitlab-ce!20246 should be addressed:

• @timzallmann started a discussion:

  EE-Port gitlab-org/gitlab-ee!6326

• @fatihacet started a discussion: (+1 comment)

  Is this && this.mergeRequestTabPanes.querySelectorAll really needed?

  If we have the this.mergeRequestTabPanes the querySelectorAll will always be defined, no?

• @fatihacet started a discussion: (+4 comments)

  Why do we need to check the existence of click?