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Array.apply(null, Array(7)).map((item, index) => ("Day" + index));
// ["Day0","Day1","Day2","Day3","Day4","Day5","Day6",]
// -- OR --
Array.from({length: 7}, (item, index) => ("Day" + index));
// ["Day0","Day1","Day2","Day3","Day4","Day5","Day6",]
// -- OR --
Array(n).fill(0)
// ES2015 Array method fill(), for n=5, output is [0,0,0,0,0]