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

0/2  =  0    =  0  |0  =  0
1/2  =  0.5  =  0.5|0  =  0
2/2  =  1    =  1  |0  =  1
3/2  =  1.5  =  1.5|0  =  1
4/2  =  2    =  2  |0  =  2
5/2  =  2.5  =  2.5|0  =  2
6/2  =  3    =  3  |0  =  3
7/2  =  3.5  =  3.5|0  =  3

Treat |0 as Math.floor

---

In code this could look like this:

for (let i = 0; i < a.length * 2; i++) {
  a[i] = a[i / 2 | 0]
}

Because immutability is preferable, one could do something like this:

function repeatItems(a, n) {
  const b = new Array(a.length * n)
  for (let i = 0; i < b.length; i++) {
    b[i] = a[i / n | 0]
  }
  return b
}

Unreadable ES6 spaghetti code:

const repeatItems = (a, n) => Array.from(Array(a.length * n), (_, i) => a[i / n | 0])