lib.d.ts

   1 type ObjectKeys<T> =
   2   T extends object
   3     ? `${Exclude<keyof T, symbol>}`[]
   4     : T extends number
   5       ? []
   6       : T extends any | string
   7         ? string[]
   8         : never
   9
  10 interface ObjectConstructor {
  11   keys<T> (o: T): ObjectKeys<T>
  12 }