I assumed these would be equal:
new Array(1).fill(0); // [0]
new Array(1).map(x => 0); // [undefined]
Why doesn't map work in the second case?
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Leo Jiang
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Because `new Array(1)` is an array with _one empty index_. The array has a length of 1 but it doesn’t have the property `0`, so there’s nothing to iterate over. – Sebastian Simon Mar 01 '16 at 07:21
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It does work. It just doesn't do what you think it does, because `map` skips "holes". – Mar 01 '16 at 07:21
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You can refer polyfill on following post [MDN - Array.map](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/map) for more information – Rajesh Mar 01 '16 at 07:24