Issue #3427181: Rework the javascript.

Closes #3427181

added 7 commits

• cfe4c0fe - Issue #3422505: Use once().
• 3d122d56 - Merge branch '3422505-once-and-context'
• 79fb2e42 - Issue #3427181: Use single quotes in js.
• dde54698 - Issue #3427181: Remove pointless `click = false`.
• bf53a06d - Issue #3427181: Early return if click != false.
• 94ce51c6 - Issue #3427181: Split unsavedChangesExist() out of main function.
• bd8e0dc0 - Issue #3427181: Remove unused drupalSettings parameter.

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