typescript: interface for fixed size array

Question

Is there a way in typescript define fixed size array. say, for example, in a function definition, I need to able to say

coord: (c:any) => number[]; //how to say it is an array of size 4

can I define an interface like we define a hash map

//this doesn't work
interface IArray{
  [number]
}

and also restrict max length to be 4.

Answer 1

You could return a tuple instead of an array:

type array_of_4 = [number, number, number, number];

var myFixedLengthArray :array_of_4 = [1,2,3,4];

// the tuple can be used as an array:
console.log(myFixedLengthArray.join(','));