class Point {
  constructor(x, y) {
    this.x = x;
    this.y = y;
  }

  add (){
    this.x = this.x ? this.x : 1;
    this.y = this.y ? this.y : 2;
    return this.x + this.y;
  }
}
const PI = 3.1415926;
exports.Point = Point;
exports.PI = PI;
let a = new Point();
console.log(a.add());

let {Point,PI} = require('./test.js');
class Point2 extends Point{

  //add();
}

let b = new Point2();
console.log(b.add());
console.log(PI);

 "babel": {
  "presets": ["es2015"]
 },
 "scripts": {
  "start": "node app/51job.js",
  "build": "babel src -d app"
 },

npm install --save-dev babel-cli
npm install babel-preset-es2015 --save-dev