This is json: [{"continent":"Pacific","country":"French Polynesia","city":"Tahiti"},{"continent":"America","country":"United States of America","city":"Adak"},{"continent":"Pacific","country":"United States of America","city":"Honolulu"},{"continent":"Pacific","country":"French Polynesia","city":"Marquesas"},{"continent":"Pacific","country":"French Polynesia","city":"Gambier"}]

There are multiple continent with same name. I want unique name on dropdown and selecting any continent get related city and based on city get Country, How using javascript?

I want: Select Unique Continent->based on continent get Unique city-> and based on city get Unique Country.