lodash.get-like-typescript-function.ts

const ENMessages = {
  "welcome": "Welcome",
  "default": {
    "login": "Login",
    "email_login": "Email login",
    "social_login": "Social login",
    "web3_login": "Web3.0 login",
    "logout": "Logout",
    "account": "Account",
    "create_account": "Create an account",
    "search_your_want": "Search your want",
    "test": {
      "aa": "AA"
    }
  },
  "products": {
    "label": "dddd"
  }
}

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)];

type ENMessageKeys = NestedKeyOf<typeof ENMessages> | '';

function getDeepValue(path: ENMessageKeys) {
  if (path === '') {
    return 'NULL'
  }
  return path.split('.').reduce((acc: any, current: string) => {
    return (acc && acc[current]) ? acc[current] : path
  }, ENMessages)
}

with-loadsh.get.ts

import get from 'lodash.get';

const language = {
  "test test": "test test",
  "search": "搜索",
  "home": {
    "home": "首页",
    "hot_brands": "热门品牌",
    "new_products": "最新商品",
    "discount": "限时折扣"
  },
  "products": {
    "Product": "Product"
  }
}

const isString = <T = any>(str: string | T): str is string => typeof str === "string";

/**
* Common utils
*/
type Primitives = string | number | symbol;


/**
* If first argument is empty string, avoid using dot (.)
* If first argument is non empty string concat two arguments andput dot (.)
* between them
*/
type Concat<Fst, Scd> =
  Fst extends string
  ? Scd extends string
  ? Fst extends ''
  ? `${Scd}`
  : `${Fst}.${Scd}`
  : never
  : never
{
  //   type Test = Concat<'hello', 'bye'> // "hello.bye"
}

/**
* Obtain union of all possible paths
*/
type KeysUnion<T, Cache extends string = ''> =
  T extends Primitives ? Cache : {
    [P in keyof T]:
    | Concat<Cache, P>
    | KeysUnion<T[P], Concat<Cache, P>>
  }[keyof T]

{
  //   // "user" | "user.description" | "user.description.name" | "user.description.surname"
  //   type Test = KeysUnion<typeof language> // eslint-disable-line

}

/**
 * @see https://stackoverflow.com/questions/68387436/is-it-possible-to-create-object-key-path-string-autocomplete-for-an-object-purel
 * @example t('home.hot_brands')
 */
export default function t(keys: KeysUnion<typeof language, "">) {
  const value = get(language, keys)
  return isString(value) ? value : keys
}

const ENMessages = {
  "welcome": "Welcome",
  "default": {
    "login": "Login",
    "email_login": "Email login",
    "social_login": "Social login",
    "web3_login": "Web3.0 login",
    "logout": "Logout",
    "account": "Account",
    "create_account": "Create an account",
    "search_your_want": "Search your want",
    "test": {
      "aa": "AA"
    }
  },
  "products": {
    "label": "dddd"
  }
}

type NestedKeyOf<T> =
  { [K in keyof T & (string)]: T[K] extends object ? K | `${K}.${NestedKeyOf<T[K]>}`: K}[keyof T & (string)];

type ENMessageKeys = NestedKeyOf<typeof ENMessages>;

function getDeepValue(path: ENMessageKeys) {
  //
}

getDeepValue('default.test.aa') // valid
getDeepValue('default.test.a')  // invalid