Once the decision has been made that Node 6 is no longer supported, it is then possible to refactor the code so that it uses appropriate modern idioms, such tha

Once the decision has been made that Node 6 is no longer supported, it is then possible to refactor the code so that it uses appropriate modern idioms, such that the external behaviour is unchanged for Node 6+ but will no longer be parsable by Node 5. In this specific case, it is both a refactor and a breaking change.