javascript class instance object literal

Question

Is there a shorthand way to add properties to an instance of a class in javascript?

Edit: The duplicate answers are about adding properties to an object not a class. I'm trying to make it easy for the user to add about 10-20 properties. I'm also trying to make sure they can't add their own properties but can only add values to the predefined properties. I don't know how to do that.

I have a javascript "class":

function Car(){
this.make="";
this.model="";
//...
}

To create an instance and add properties I would use:

var mycar = new Car();
    mycar.make="honda";
    mycar.model="civic";
    //...

Is there a shorthand way to create an instance and add the properties so I don't have to type "mycar." each time?

Answer 1

If your constructor doesn't do anything important, you can use Object.create():

function Car() {
  //...
}

console.log(
  Object.create(
    Car.prototype,
    Object.getOwnPropertyDescriptors(
      { make: 'honda', model: 'civic' }
    )
  )
);

I wouldn't exactly call this "shorthand", but it is a single statement, and it omits invoking Car() if your constructor's body is redundant.

I'd personally recommend using Object.assign() within the body of your constructor:

function Car(props) {
  /* to formally mimic behavior of default parameters specification */
  // props = arguments.length < 1 || props === undefined ? {} : props;
  /* commonly used "good-enough" ES5 equivalent */
  props = props || {};
  Object.assign(this, props);
}

console.log(
  new Car({ make: 'honda', model: 'civic' })
);

Or ES6:

class Car {
  constructor (props = {}) {
    Object.assign(this, props);
  }
}

console.log(
  new Car({ make: 'honda', model: 'civic' })
);