addUnsavedChanges() will save same id multiple times

[liffiton]

addUnsavedChanges() was intended to avoid saving the same id multiple times (the comment says "Don't add duplicate state"), but it still does. This means that multiple calls to addUnsavedChanges() with a given id followed by one call to removeUnsavedChanges() with that same id will leave other copies of the id in the array, and the beforeunload listener will still be active.

The issue is that the condition here is always true.

Instead of !indexOf(id) > -1 it should be !(indexOf(id) > -1), I believe.