sparse array

Question

What does the code snippet to the right output by console.log?

Snippet

const arr = [1,,,2]

// forEach
arr.forEach(i => console.log(i))

// map
console.log(arr.map(i => i * 2))

// for ... of
for (const i of arr) {
  console.log(i)
}

// spread
console.log([...arr])

Source

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