[ahoge]

  > new Array('a')
  ["a"]
  > new Array(2, 3)
  [2, 3]
  > new Array(2)
  [undefined, undefined]
  > new Array(2.3)
  RangeError: invalid array length
  > new Array(2.3, 4.5)
  [2.3, 4.5]

The Array constructor is really bogus. It switches to a different mode if a single number is passed.

ES6 added `Array.of` for this reason:

  > Array.of()
  []
  > Array.of(1)
  [1]
  > Array.of(1, 2)
  [1, 2]

I don't really think it's needed though. Spread and rest already take care of the common use cases.