var x = `{"2018-06-28":{"may":3,"april":4, "june":6},"2018-07-04":{"may":2,"april":3, "june":7}, "2018-07-11":{"may":4,"april":5, "june":8}}`
"2018-07-11":{"may":4,"april":5, "june":8}
var response = '{"2018-06-28":{"may":3,"april":4, "june":6},"2018-07-04":{"may":2,"april":3, "june":7}, "2018-07-11":{"may":4,"april":5, "june":8}}';
var json = JSON.parse(response);
var date = [];
for (var item in json) {
date.push(new Date(item).getTime());
}
var actual = date.reduce(function(prev, next) {
return prev > next ? prev : next;
}, 0);
console.log(new Date(actual).toLocaleDateString()); //> 2018-07-11