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Why does this code produce an array of 20 elements which are all undefined:

> Array(20).map(function() { return 3; })
[ , , , , , , , , , , , , , , , , , , ,  ]

Whereas this code produces an array of 20 elements which are all 3s:

> Array(20).join(' ').split(' ').map(function() { return 3; })
[ 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3 ]

Why does the first approach not behave as expected?

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    map does omit holes. Commented Aug 25, 2015 at 22:38
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