property names of multidimensions array duplicative

const getPropertyNames = (arr = []) => arr.length > 0 ? Object.keys(arr[0]) : [];

const data = [ { "name": "Tiger Nixon", "position": "System Architect", "salary": "320800", "start_date": "2011\/04\/25", "office": "Edinburgh", "rating": "5421" }, { "name": "Garrett Winters", "position": "Accountant", "salary": "170750", "start_date": "2011\/07\/25", "office": "Tokyo", "rating": "8422" }, { "name": "Ashton Cox", "position": "Junior Technical Author", "salary": "86000", "start_date": "2009\/01\/12", "office": "San Francisco", "rating": "1562" }, { "name": "Cedric Kelly", "position": "Senior Javascript Developer", "salary": "433060", "start_date": "2012\/03\/29", "office": "Edinburgh", "rating": "6224" } ];
console.log( getPropertyNames(data) );