Array.from does not accept Iterable<T>|ArrayLike<T> argument

[Jessidhia]

TypeScript Version: 2.6.2

Code

function takeN<T> (n: number, input: Iterable<T>|ArrayLike<T>): [T[], T[]] {
  const array = Array.from(input)
  return [array.splice(0, n), array]
}

function takeNv2<T> (n: number, input: Iterable<T>|ArrayLike<T>): [T[], T[]] {
  const array = isIterable(input) ? Array.from(input) : Array.from(input)
  return [array.splice(0, n), array]

  function isIterable(arg: any): arg is Iterable<any> {
    return Symbol.iterator in arg
  }
}

Playground link

Expected behavior:

takeN to work

Actual behavior:

takeN raises an error on Array.from, because TypeScript does not accept that the input matches more than one overload.

This is either a compiler bug, or the declaration for Array.from needs an overload that accepts either.

[mhegazy]

The root cause is #14107.
We can work around this by adding an overload for Array.from to accept ArrayLike<T> | Iterable<T> instead of just Iterable<T>.

A similar bug report was #20215 for Date constructor.

[DanielRosenwasser]

Thanks @Kovensky!