How to refactor an object from ES5 to ES6

ES5 to ES6

### ES5:

var Rectangle = function (w, h) {
  	this.width = w;
  	this.height = h;

    this.area = function() {
 		   return calcArea();
    }

    var calcArea = function() {
        return this.height * this.width;
    }
}

### ES6:

const calcArea = () => {
    return this.height * this.width;
}

class Rectangle {

    constructor(w, h) {
        this.width = w;
        this.height = h;
    }

    area() {
      return calcArea();
    }

}

### Usage

var r = new Rectangle(10, 40);

console.log(r.width) // 10;

console.log(r.area()) // 400;

console.log(r.calcArea()) // Error 

webpack can translate from ES6 to ES5