How to use spread syntax or destructuring into `this` value?

Question

I know we can do something like:

const a = { b: 1, c: 2 }

const A = { ...a };
// A { b: 1, c: 2 }

But how do we use this approach to pass data into this value?

For example we have a class A {} and want to dynamically set object property into this. The usual way would be using Object.defineProperties with maybe for...in loop:

const a = { b: 1, c: 2 }

class A {
  constructor(obj){
    for (const k in obj)
      Object.defineProperty(this, k, { value: obj[k] });
  }
}

new A(a);
// A { b: 1, c: 2 }

So I'm thinking, since we have the syntactic sugar now, how can we utilise it to the example above?

EDIT

I am talking about spread operator syntax ... here.

Answer 1

You can't update this by spreading and then assigning the result.

You can use Object.assign() to copy properties from the obj to this:

class A {
  constructor(obj) {
    Object.assign(this, obj);
  }
}

const a = { b: 1, c: 2 }

console.log(new A(a));

You can use destructuring to assign known properties to this:

class A {
  constructor(obj) {
    ({ b: this.b, c: this.c } = obj);
  }
}

const a = { b: 1, c: 2 }

console.log(new A(a));