TypeScript系列教程九《类型转换》-- 索引访问类型

type Person = { age: number; name: string; alive: boolean };
type Age = Person["age"];

//type Age = number

type I1 = Person["age" | "name"];
     
//type I1 = string | number

type I2 = Person[keyof Person];
     
//type I2 = string | number | boolean

type AliveOrName = "alive" | "name";
type I3 = Person[AliveOrName];
     
//type I3 = string | boolean

type I1 = Person["alve"];
//Property 'alve' does not exist on type 'Person'.

const MyArray = [
    { name: "Alice", age: 15 },
    { name: "Bob", age: 23 },
    { name: "Eve", age: 38 },
  ];
  
  type Person = typeof MyArray[number];
         
//   type Person = {
//       name: string;
//       age: number;
//   }
  type Age = typeof MyArray[number]["age"];
       
//   type Age = number
  // Or
  type Age2 = Person["age"];
        
//   type Age2 = number

const key = "age";
type Age = Person[key];
//Type 'any' cannot be used as an index type.
//'key' refers to a value, but is being used as a type here. Did you mean 'typeof key'?

type key = "age";
type Age = Person[key];