TypeScript keyof All In One

keyof

generic

https://www.typescriptlang.org/docs/handbook/2/keyof-types.html

TypeScript 允许我们遍历某种类型的属性，并通过 keyof 操作符提取其属性的名称。
keyof 操作符是在 TypeScript 2.1 版本引入的，该操作符可以用于获取某种类型的所有键，其返回类型是联合类型。

interface Person {
  name: string;
  age: number;
  location: string;
}

type K1 = keyof Person; 
// type K1 = keyof Person

type K2 = keyof Person[];  
// type K2 = keyof Person[]

type K3 = keyof { [key: string]: Person };  
// type K3 = string | number

as keyof

enum HTTPTypes {
  get = 'get',
  post = 'delete',
  put = 'put',
  delete = 'delete',
}

const HTTP: {
  // [key: string]: any,
  [key: string]: string,
} = {};

for (let key in HTTPTypes) {
  console.log('key =', key);
  HTTP[key] = HTTPTypes[key as keyof object];
  // Element implicitly has an 'any' type because expression of type 'string' can't be used to index type 'typeof HTTPTypes'.
  // HTTP[key] = HTTPTypes[key];
}

https://stackoverflow.com/questions/57086672/element-implicitly-has-an-any-type-because-expression-of-type-string-cant-b

refs

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