Passing object with predefined props to class constructor es6

Question

I am trying to pass to my class constructor an object with predefined properties.

like this

class Test {

constructor({
    a = "test a",
    b = "test b"
    }) {

    }
}

PS I know how to define properties of objects. I want to know how to predefine properties.

Answer 1

It seems you want to pass one object to the constructor and have its properties assigned to single keys of the class. You can use destructuring for that this way:

class MyClass {
  constructor({a,b} = {a:1,b:2}) {
    this.a = a;
    this.b = b;
  }
}

Be aware that this is not safe for partially filled objects:

var instance = new MyClass({a:3});
// instance.b == undefined

Handling this could be done like so:

class MyClass {
  constructor({a=1,b=2} = {}) {
    this.a = a;
    this.b = b;
  }
}

Which results in:

var instance = new MyClass({a:3});
// instance.a == 3
// instance.b == 2

Answer 2

Like I said in my comment, there's an example right at the top of the documentation .

class Test {
    constructor(/* put arguments here if you want to pass any */){
        //Pre-define a and b for any new instance of class Test
        this.a = "test a";
        this.b = "test b";
    }
}

Answer 3

The simple solution would be to pass the constructor and object during instantiation:

 class Test { constructor(obj){ this.a = obj.a; this.b = obj.b; } }; const obj = { a: 'value', b: 'value' }; const newtTest = new Test(obj);