Why can I not invoke Array.prototype.map directly on this Array instance?

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Why can I not invoke Array.prototype.map directly on Array instance o?

var o = Array(3); // [ undefined, undefined, undefined ]
o.map((x,y) => y*2); //  [ undefined, undefined, undefined ]

Instead, I have to use apply (or call):

Array.apply(0, o).map((x, y) => y*2)); // [ 0, 2, 4 ]

What am I missing?

Finally, an alternative to the above is:

[...o].map((x, y) => y*2); // [ 0, 2, 4]

I presume because this corrects whatever is missing in my original implementation.

asked 49 secs ago

Ben Aston

8,550

Why can I not invoke Array.prototype.map directly on this Array instance?