Create class instance from plain object without manual constructor

Question

Is it possible to create a class instance from a plain object without manually mapping plain object values to class instance variables?

For example:

class Person {
  id;
  firstName;
  lastName;
  age;

  fullName() {
    return `${this.firstName} ${this.lastName}`;
  }
}

const hemmingway = {
  id: 1,
  firstName: "Ernest",
  lastName: "Hemmingway",
  age: 62
};

Is it possible to create a Person class instance out of hemmingway without having to resort to manually mapping the keys like this:

constructor(plainObject) {
      this.id = plainObject.id;
      this.firstName = plainObject.lastName;
      this.lastName = plainObject.lastName;
      this.age = plainObject.age;
}

This would be extremely helpful when trying to map network API response objects to class instances.

CertainPerformance · Accepted Answer · 2018-09-03 07:55:50Z

After passing the object, use Object.assign to assign all of its properties to the instantiation:

class Person {
  id;
  firstName;
  lastName;
  age;
  constructor(plainObject) {
    Object.assign(this, plainObject);
  }
  fullName() {
    return `${this.firstName} ${this.lastName}`;
  }
}

const hemmingway = {
  id: 1,
  firstName: "Ernest",
  lastName: "Hemmingway",
  age: 62
};
const personHemmingway = new Person(hemmingway);
console.log(personHemmingway.fullName());

Of course, you could also do it outside of the constructor:

class Person {
  id;
  firstName;
  lastName;
  age;
  fullName() {
    return `${this.firstName} ${this.lastName}`;
  }
}

const hemmingway = {
  id: 1,
  firstName: "Ernest",
  lastName: "Hemmingway",
  age: 62
};
const personHemmingway = new Person();
Object.assign(personHemmingway, hemmingway);
console.log(personHemmingway.fullName());

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