Typescript interface for an array

Question

This seems like a dumb question, but here I am.

I know an interface can be used to define an object and its keys, but how do I make an interface if that object is an array?

For example, the interface for

const object = {
   bar: 1
   foo: 2
}

would be

interface myInterface {
   bar: number
   foo: number
}

What if my object is:

const object = [[1,2,3],[4,5,6],[7,8,0]]

What about a 3D array?

How do I define this interface?

it depends how precise you want to be, but first let me say that in for example vscode, just hovering over 'object' will tell you it's a number[][], a 3d array would be like number[][][]. As mentioned you can use tuples to be more restrictive about the length of the array, and account for different types in different positions — Countingstuff
– Countingstuff, Commented Oct 20, 2020 at 23:06

pzaenger · Accepted Answer · 2020-10-20 23:11:56Z

4

You could use tuples:

const object: [
  [number, number, number],
  [number, number, number],
  [number, number, number]
] = [[1,2,3],[4,5,6],[7,8,0]];

Or using a type additionally:

type Point3D = [
  [number, number, number],
  [number, number, number],
  [number, number, number]
];

const object: Point3D = [[1,2,3],[4,5,6],[7,8,0]];

Note: Point3D is restricted to exactly three times [number, number, number].

edited Oct 20, 2020 at 23:11

answered Oct 20, 2020 at 23:04

pzaenger

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1 Comment

Andrew Zaw Over a year ago

This is what I was looking for, thanks. I figured the answer was going to be very very simple.

Henry · Accepted Answer · 2020-10-20 23:06:13Z

2

You can define a type for that, for example:

type MyArray = number[][];

To hold a 2D array of numbers.

Or you can use the tuple type if you want your arrays to have a set length or hold values of different types in different positions:

type MyArray = [number, number, number][];

answered Oct 20, 2020 at 23:06

Henry

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