[Typescript] Index access types

本文主要是介绍[Typescript] Index access types，对大家解决编程问题具有一定的参考价值，需要的程序猿们随着小编来一起学习吧！

Indexed Access types provide a mechanism for retrieving part(s) of an array or object type via indices. We’ll look at how this kind of type works, and a couple of practical examples of where you might use them.

interface Car {
  make: string
  model: string
  year: number
  color: {
    red: string
    green: string
    blue: string
  }
}

We can get color type:

let carColor: Car["color"]
/*
let carColor: {
    red: string;
    green: string;
    blue: string;
}
*/

We can get nested prop type:

let carColorRedComponent: Car["color"]["red"] // string

Index access type has safe guard:

let carColor: Car["not-something-on-car"] // ERROR: Property 'not-something-on-car' does not exist on type 'Car'.

We can get Intersection types on index access types:

let carPropertyWeInterest: Car["color" | "year", "model"]
/*
string | number | {
    red: string;
    green: string;
    blue: string;
}
*/

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