Woocommerce Postcode dropdown list based on selected State

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I want to return Woocommerce postcodes as a dropdown list like in this Stackoverflow thread Change postcode shipping field to a dropdown in Woocommerce (which works well but is returned on all countries & states); I want to add the condition that it should be returned only based on the selected State by the user. For instance if someone selects State1 they get a certain dropdown list of Postcodes defined in that state only, and if they select another state2 they get a dropdown of another list of postcodes in that state only as well, and the rest of undefined States can remain to default function without dropdown.

Any help will be appreciated.