Defining type string | undefined inside an Type of array of strings

Question

I have custom types which is the following:

hero?: string
power?: string

I want to add those type into an array, which is part of another type

type Superheroes = {
character: string[] | []
villains: number | null
city: string

}

When I try to use the type (see below) I get the following error Typescript: Type 'string | undefined' is not assignable to type 'string'

return {
character: [hero, power],
villains: 2 || null,
city: 'new york' || null
}

What is the correct way to define hero and power types inside the character array?

Could you make an edit in the example please tsplay.dev/mL9MKW ? — Roman A.
– Roman A., Commented Jun 1, 2021 at 15:12

aleksxor · Accepted Answer · 2021-06-01 18:24:22Z

1

To make it assignable you should define your Superheroes type like that:

type Superheroes = {
  character: (string | undefined)[]
  villains: number | null
  city: string
}

or if there are always no more than two elements in character array:

type Superheroes = {
  character: [string?, string?]
  villains: number | null
  city: string
}

TS playground

answered Jun 1, 2021 at 18:24

aleksxor

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Comments

Mohamed Ayadi · Accepted Answer · 2021-06-01 15:23:07Z

0

You can change the type to :

city: string || null

or change the assign of the city attribute to :

city: 'new york'

without the array or null.

answered Jun 1, 2021 at 15:23

Mohamed Ayadi

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2 Comments

user6248190 Over a year ago

The issue is with the hero and power types inside the character array. The city being an array was a typo which is now fixed

Mohamed Ayadi Over a year ago

oh ok. I see that you add question mark to hero?: string and power?: string without initialization and that could be undefined, I think you can try initialization hero and power like this: hero?: string = ''; power?: string = ''; to avoid the error.

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