class-transformer-demo.ts

import "es6-shim";
import "reflect-metadata";
import {deserializeArray, Expose, plainToClass, Transform, Type} from "class-transformer";

export function Default(defaultValue: any) {
  return Transform((value: any) => (value !== null && value !== undefined ? value : defaultValue));
}

export class Pet {
  name: string;
}

export class Petc {
  name: string;

  constructor(data: Pet) {
    this.name = data.name;
  }

}

export class User {
  id: number;
  firstName: string;
  lastName: string;
  age: number;

  @Expose()
  @Default([])
  @Type(() => Pet)
  pets: Pet[];
}

export class Userc {
  id: number;
  firstName: string;
  lastName: string;
  age: number;
  pets?: Pet[];

  constructor(data: Userc) {
    this.id = data.id;
    this.firstName = data.firstName;
    this.lastName = data.lastName;
    this.age = data.age;
    this.pets = data?.pets?.map(pet => new Petc(pet)) || [];
  }
}

const userJson = [{
  "id": 1,
  "firstName": "Johny",
  "lastName": "Cage",
  "age": 27,
  "unkownProp": 'hello there',
  "pets": [{"name": "Miky"}]
},
  {
    "id": 2,
    "firstName": "Ismoil",
    "lastName": "Somoni",
    "age": 50,
  },
  {
    "id": 3,
    "firstName": "Luke",
    "lastName": "Dacascos",
    "age": 12,
    "pets": [{"name": "Miky"}]
  }]

let users = deserializeArray(User, JSON.stringify(userJson));
const usersc =  userJson.map(user => new Userc(user));
console.log(userJson[0] instanceof User)
console.log(userJson[0] instanceof Object)
console.log()
console.log(users[0] instanceof User)
console.log(users[0] instanceof Userc)
console.log(users[0] instanceof Object)
users[0].pets.push(plainToClass(Pet, {"name": "Tom"}))
console.log()
console.log(usersc[0] instanceof User)
console.log(usersc[0] instanceof Userc)
console.log(usersc[0] instanceof Object)
usersc[0].pets.push(new Petc({"name": "Tom"}))
console.log()
console.log(users);
console.log()
console.log(usersc);

console.log(users[0].pets[0] instanceof Pet)
console.log(usersc[0].pets[0] instanceof Petc)