Why is the value of
(new Array(2)).map(function (x, i, a) { return i })
[undefined, undefined] instead of [0, 1]?
Why is the value of (new Array(2)).map(function (x, i, a) { return i })
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Why is the value of
(new Array(2)).map(function (x, i, a) { return i })
[undefined, undefined] instead of [0, 1]?
new Array(2)generates a sparse array – with no values, but of length 2. It is equivalent to[,,].Now, Array’s
.map()method is specified to leave out uninitialised/deleted indices, so you just get back another empty array.Related question on what you want to do: How to write List/Array comprehensions in JavaScript