lodash-es-demo.ts

import { get } from "lodash-es";

interface Person {
  name: string;
  age: number;
  children?: Person[];
}

declare type DriverType = "Race" | "Commercial" | "Personal";

interface Driver extends Person {
  type: DriverType;
  car: Car;
}
interface Car {
  make: string;
  model: string;
  year: number;
}
interface ToyCar {
  brand: string;
}
interface NumericCarDict<T> {
  [key: number]: T;
}

const person: Person = {
  name: "Bob",
  age: 41
};

const civic: Car = {
  make: "Honda",
  model: "Civic",
  year: 2001
};

const forester: Car = {
  make: 'Subaru',
  model: 'Forester',
  year: 2015
};

const bobDriver: Driver = {
  ...person,
  type: "Personal",
  car: civic
};

const hotWheel = {
  brand: 'Hotwheels'
};

const carDict: NumericCarDict<Car> = {
  0: civic,
  1: forester
};

const anyObj: any = {
  really: 'yes'
};

let undefinedVar: undefined;
let nullVar: null = null;

/*
  get<TObject extends object, TKey extends keyof TObject>(
    object: TObject,
    path: TKey | [TKey]
  ): TObject[TKey];
*/
const tObjProp: Car = get<Driver, "car">(bobDriver, "car");

/**
  get<TObject extends object, TKey extends keyof TObject>(
    object: TObject | null | undefined,
    path: TKey | [TKey]
  ): TObject[TKey] | undefined;
 */
const tObjOrNull: Car | undefined = get<Driver, "car">(bobDriver, "car");

/**
  get<TObject extends object, TKey extends keyof TObject, TDefault>(
    object: TObject | null | undefined,
    path: TKey | [TKey],
    defaultValue: TDefault
  ): TObject[TKey] | TDefault;
 */
const withDefault: Car = get<Driver, "car", Car>(bobDriver, "car", {
  make: "Ford",
  model: "Mustang",
  year: 2018
});

const defaultOtherType: Car | ToyCar = get<Driver, "car", ToyCar >(bobDriver, "car", hotWheel);

/**
  get<T>(
    object: NumericDictionary<T>,
    path: number
  ): T;
 */
const dictGet: Car = get<Car>(carDict, 0);

/**
  get<T>(
    object: NumericDictionary<T> | null | undefined,
    path: number
  ): T | undefined;
 */
const dictGetNull: Car | undefined = get<Car>(carDict, 4);
const dictGetNull2: Car | undefined = get<Car>(nullVar, 4);
const dictGetNull3: Car | undefined = get<Car>(undefinedVar, 4);

/**
  get<T>(
    object: NumericDictionary<T> | null | undefined,
    path: number,
    defaultValue: TDefault
  ): T | TDefault;
 */
const dictGetWithDefault: Car | ToyCar = get<Car, ToyCar>(carDict, 4, hotWheel);
const dictGetWithDefault2: Car | ToyCar = get<Car, ToyCar>(nullVar, 4, hotWheel);
const dictGetWithDefault3: Car | ToyCar = get<Car, ToyCar>(undefinedVar, 4, hotWheel);


/*
  get<TDefault>(
    object: null | undefined,
    path: PropertyPath,
    defaultValue: TDefault
  ): TDefault;
*/
const alwaysDefaultNull: ToyCar = get<ToyCar>(nullVar, 'brand', hotWheel);
const alwaysDefaultUndefined: ToyCar = get<ToyCar>(undefinedVar, 'brand', hotWheel);


/**
get(
    object: null | undefined,
    path: PropertyPath
): undefined;
*/
const alwaysUndefinedNull: undefined = get(nullVar,'property.path.to.thing');
const alwaysUndefined: undefined = get(undefinedVar,'property.path.to.thing');


/**
  get(
    object: any,
    path: PropertyPath,
    defaultValue?: any
  ): any;
 */
const getAny: any = get(anyObj, 'really', 104); // nothing matters anymore