Using Typescript to define arrays with distinct data types for each element

I'm looking to create a typed array where each element is made up of different data types, eliminating the need for manual casting. Currently, I have an array called 'cases' that contains arrays with a string as the first element and a boolean as the second.

const cases = [
  [ 'http://gmail.com', false ],
  [ '/some_page', true ],
  [ 'some_page', false ]
]

describe("'isInternalLink' utility", () => {
  test.each(cases)(
    "given %p as argument, returns %p", (link, result) => {
      expect(
        isInternalLink(<string>link)
      ).toEqual(
        <boolean> result
      )
    }
  )
})

Instead of having an array of 'string | boolean' type, I want to specify separate data types for the first and second elements in each array within 'cases'.

If you have any suggestions on how to achieve this efficiently, please let me know!

arraystypescriptcastingjestjs

Answer №1

cases is an Array, with each element within the array being a Tuple. If you define cases in one of these two ways:

const cases: [string, boolean][] = ...

...or in this alternative way:

const cases: Array<[string, boolean]> = ....

...then link will have a type of string and result will have a type of boolean. This allows for simplification of your test as follows:

describe("'isInternalLink' utility", () => {
  test.each(cases)(
    "given %p as argument, returns %p", (link, result) => {
      expect(isInternalLink(link)).toEqual(result)
    }
  )
})

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