How to reference array values from array defined in interface?

Question

I am new to TypeScript. I have the following interface defined:

interface Cities {
    names: ["New York", "Chicago", "Los Angeles"]
    // rest of the parameters
}

Now I have a function which takes in a parameter city which should only be the ones defined in names:

const getPopulation = (name: Cities["names"]) => {
    // return population of city 'name'
}

However, the above would/does not work since Cities["names"] is an array. I want to reference the array values (i.e. "New York" etc.). How would I be able to do this?

Sounds like you should be using an enum instead.

Terry
– Terry

2021-06-07 22:26:56 +00:00
Commented Jun 7, 2021 at 22:26 — Terry
– Terry, Commented Jun 7, 2021 at 22:26

yaritaft · Accepted Answer · 2021-06-07 22:25:37Z

2

I would do

enum City {
  NewYork="New York";
  Chicago="Chicago";
  LosAngeles="Los Angeles";
}
const getPopulation = (name: City): number => {
    // return population of city 'name'
}

Or you can do this

type City = "New York" | "Chicago" | "Los Angeles"
const getPopulation = (name: City): number => {
    // return population of city 'name'
}

Please let me know if this is useful. I didn't fully understand the question. But I think you are trying to enforce that name is not just an string, It has to be a string inside and group of options. If you can provide further details It would be great to help you better!

answered Jun 7, 2021 at 22:25

yaritaft

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1 Comment

user12055579 Over a year ago

I was looking more for getting the array values union since the Cities interface has more parameters. But this was still helpful to know enum. Thanks!

akuiper · Accepted Answer · 2021-06-07 22:27:20Z

1

Cities["names"] gives a tuple type which you can further convert to a union type using Cities['names'][number] as function parameter:

const getPopulation = (name: Cities["names"][number]) => {
    // return population of city 'name'
}

See playground

answered Jun 7, 2021 at 22:27

akuiper

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