TypeScript Utility: keyof nested object

In this blog post, we will learn how to build a TypeScript util type, that exposes all the key paths of an object, including the nested ones.

Typescript: NestedKeyOf

• Utility of nested objects

  type NestedKeyOf<ObjectType extends object> =
    {[Key in keyof ObjectType & (string | number)]: ObjectType[Key] extends object
      ? `${Key}` | `${Key}.${NestedKeyOf<ObjectType[Key]>}`
      : `${Key}`
    }[keyof ObjectType & (string | number)];
  declare function sortBy<T extends object>(person: T, sort: NestedKeyOf<T>)
   
  const person = {
    name: 'bob',
    age: 30,
    dog: {
      owner: {
        name: 'mydog'
      }
    }
  }
  sortBy(person, 'dog.owner.name'); // <- typescript shows valid options