TypeScript - how to type a multi dimension array that has different shapes

Question

I have a two dimensional array which can have different shapes and can contain either numbers or string. How can I create an interface for that?

Examples:

// example one
[[0]]

// example two
[
  [0, 'I', 0, 0],
  [0, 'I', 0, 0],
  [0, 'I', 0, 0],
  [0, 'I', 0, 0],
]

// example three
[
  [0,   'J', 0],
  [0,   'J', 0],
  ['J', 'J', 0],
]

This worked but for a full reveal the examples above are part of an object with other properties so in my case I needed to do a bit more to get rid of some typescript errors but this does the trick. — cbutler
– cbutler, Commented Mar 10, 2022 at 12:10

Mattia · Accepted Answer · 2022-03-10 11:33:46Z

If you want a general type for 2D arrays you can do this:

// Generic 2D array type
type Arr2DGeneric<T> = T[][];
// The trick is to read this type right to left: An array ([]) of arrays ([]) of type T

// example one
const g1: Arr2DGeneric<number|string> = [[0]]

// example two
const g2: Arr2DGeneric<number|string> = [
  [0, 'I', 0, 0],
  [0, 'I', 0, 0],
  [0, 'I', 0, 0],
  [0, 'I', 0, 0],
]

// example three
const g3: Arr2DGeneric<number|string> = [
  [0,   'J', 0],
  [0,   'J', 0],
  ['J', 'J', 0],
]

Or as @Nalin Ranjan pointed out you can do this to represent the specific type in your example:

// Specific to number | string
type NumStrArr2D = (number|string)[][];


// example one
const ns1:NumStrArr2D = [[0]]

// example two
const ns2:NumStrArr2D = [
  [0, 'I', 0, 0],
  [0, 'I', 0, 0],
  [0, 'I', 0, 0],
  [0, 'I', 0, 0],
]

// example three
const ns3:NumStrArr2D = [
  [0,   'J', 0],
  [0,   'J', 0],
  ['J', 'J', 0],
]

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