TYPESCRIPT

typescript keyof

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

type K1 = keyof Person; // "name" | "age" | "location"
type K2 = keyof Person[]; // "length" | "push" | "pop" | "concat" | ...
type K3 = keyof { [x: string]: Person }; // string

typescript keyof typeof

enum ColorsEnum {
    white = '#ffffff',
    black = '#000000',
}

type Color = keyof typeof ColorsEnum; // 'white' | 'black'

let colorLiteral: Color
colorLiteral = "white"  // OK
colorLiteral = "black"  // OK
colorLiteral = "red"    // Error...

typescript keyof object

type staffKeys = 'name' | 'salary';
function getProperty<T, K extends staffKeys>(obj: T, key: K): T[K] {
return obj[key];
}

typescript keyof type

type Arrayish = { [n: number]: unknown };
type A = keyof Arrayish;
    
type A = number
 
type Mapish = { [k: string]: boolean };
type M = keyof Mapish;
    
type M = string | number
Try