Pass array to variadic function in TypeScript

Question

I have a method that should accept either an array of numbers or accept a variable number of number arguments (variadic). In most languages I've used, when you make a method/function variadic, it accepts both, but it seems that in TypeScript, you cannot. When I make this particular function variadic, all of the places where I supply a number[] fail compilation.

Signature for reference (in class ObjectIdentifier):

constructor(... nodes : number[]) {

This fails:

return new ObjectIdentifier(numbers);

where numbers is of type number[].

Overload the constructor signatures: https://stackoverflow.com/a/12702786/6680611 — cartant, Aug 12 '18 at 13:24

score 20 · Answer 1 · answered Aug 12 '18 at 13:15

20

Use the following syntax:

const func = (...a: number[]) => console.info('a', a)

func(1, 2, 3)

func(...[1, 2, 3])

answered Aug 12 '18 at 13:15

kemsky

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score 3 · Answer 2 · answered Aug 12 '18 at 13:11

Here is one approach:

class ObjectIdentifier {
  public myNodes: number[];
  constructor(first?: number | number[], ...rest: number[]) {
    this.myNodes =
      first === undefined
        ? []
        : first instanceof Array
          ? [...first, ...rest]
          : [first, ...rest];
  }
}
const empty = new ObjectIdentifier();
const a = new ObjectIdentifier(1);
const b = new ObjectIdentifier([1]);
const c = new ObjectIdentifier(1, 2, 3);
const d = new ObjectIdentifier([1, 2, 3]);
const e = new ObjectIdentifier([1, 2, 3], 4, 5, 6);

The only quirk is seen in that last case where you can pass an array as the first parameter followed by a variable number of numbers.

This should only be used if you can't control that you are being called in both ways, otherwise just use the spread operator when passing an array — Brian Adams, Aug 12 '18 at 13:31

Pass array to variadic function in TypeScript

2 Answers2