Ensure that the 2D array of tuples in Typescript contains at least one element

In my Typescript variable declaration, I implemented a type check to ensure that all elements in an array of tuples are of length 2 and consist of numbers:

const testArea: [number, number][] = [[0, 0], [0, 220000], [220000, 220000], [220000, 0]];

This approach successfully initializes the variable, but it still permits an empty array:

const testArea: [number, number][] = []; // No error

I attempted to modify this as follows:

const testArea: [[number, number]] = [[0, 0], [0, 220000], [220000, 220000], [220000, 0]]; // error: only allows a single tuple in the array

However, this did not work for cases where there are multiple tuples in the array (although it does prevent an empty array from being valid).

Is there a way to verify that the outer array contains tuples of type [number, number] and also ensure that it contains at least one of these tuples?

arraystypescripttuples

Answer №1

A simple trick using the rest operator can solve this issue.

type Tuple = [number, number]

type NonEmptyArray<T> = [T, ...T[]];

type Data = NonEmptyArray<Tuple>

const data: Data = [] // error
const data1: Data = [[]] // error
const data2: Data = [[1]] // error
const data2: Data = [[1,1]] // Ok

Various alternatives exist to ensure that the array is not empty,

one of which is:

type NonEmptyArray2<T extends unknown[]> = T['length'] extends 0 ? never : T

For more information, you can refer to @jcalz's answer here

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