Question 50666 in Javascript Question posted in
A very good W3school tutorial can be found here.

How do I index into an array type in Typescript? – Javascript

Let’s say there is a type

type Groceries = {
  details: {
    totalCost: number;
    items: Array<{
      name: string;
      price: number;
    }>
  }
}

And I want to index into the nested type of price
to type a variable let’s say

appleCost: Groceries["details"]["items"][0]["price"]

^ this throws an error that property "items" does not exist
How can I achieve this?

Doing Groceries["details"]["items"][0]["price"] is throwing an error, I believe because it is an Array type. How can I index into the individual types defined in the Array type?

Tried indexing by doing Groceries["details"]["items"][0]["price"]

Tags:

2

Answers


  1. 0

    Integers are used as the indices of arrays. So to get the member values you index the array type with number.

    Or in your case:

    Groceries['items'][number]["price"]

    Full example:

    type Groceries = {
  totalCost: number;
  items: Array<{
    name: string;
    price: number;
  }>
}


type Something = {
    appleCost: Groceries['items'][number]["price"]
}
// `Something` is equivalent to { appleCost: number }

    See Playground

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  2. 0

    It works totally fine for me

    let appleCost: Groceries["details"]["items"][0]["price"]
//  ^?
//  let appleCost: number

let groc: Groceries
let bananaCost: typeof groc['details']['items'][0]['price']
//  ^?
//  let bananaCost: number

let price: {
    cost: Groceries["details"]["items"][0]["price"]
} = { cost: 123 }
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