CODEWITHSUNDEEP
typescript
mkoala
mkoala

Reputation: 963

How to get the Type of an Array item

If I have a type for a custom array that I get from a node_module (meaning I cant change it)

export type CustomArray = Array<
  {
    a: string;
    b: string;
  }
>

what is the proper way to define the type of one of this array`s item?

So far I figured out that that 

type CustomArrayItem = CustomArray[0]

or 

type CustomArrayItem = CustomArray[number]

works but I am unsure if this is right because I could not find anything about it in the Docs.

Upvotes: 0

Views: 134

Answers (1)

Titian Cernicova-Dragomir
Titian Cernicova-Dragomir

Reputation: 249616

As you discovered, both work well enough. I would use CustomArray[number] since that basically says 'Give me the type if I index with any number' while CustomArray[0] says 'Give me the type if I index with 0'. The two seem similar, but if CustomArray is a tuple type, results may actually be different: 

export type CustomArray = [string, ...number[]];

type I0 = CustomArray[0] // string
type I1 = CustomArray[1] // number
type INumber = CustomArray[number] // string | number

Playground Link

Upvotes: 1

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