How to duplicate elements in a js array?

Question

Whats the easiest way (with \"native\" javascript) to duplicate every element in a javascript array?

The order matters.

For example:

Answer 1

I suppose you could do:

var duplicated = a.map(function(item) {
    return [item, item];
}).reduce(function(a, b) { return a.concat(b) });

//duplicated: [2, 2, 3, 3, 1, 1, 4, 4]