Array.map doesn’t seem to work on uninitialized arrays [duplicate]

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If you’d like to fill an array, you can use Array(5).fill() and the methods will then work as expected–see the alternate related answer from aasha7. Older pre-fill approaches include:

Array.apply(null, new Array(5)).map(function() { return 0; });
// [ 0, 0, 0, 0, 0 ]

After some reading one of the posts linked in the comments, I found this can also be written as

Array.apply(null, {length: 5}).map(function() { return 0; });

However, trying to use .map on undefined values will not work.

x = new Array(10);
x.map(function() { console.log("hello"); });

// so sad, no "hello"
// [ , , , , , , , , ,  ]

.map will skip over undefined values 🙁

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