Mobx failure

mobx-babel6.js

const { observable, computed, decorate } = require('mobx');
class OrderLine {
  constructor() {
    this.price = 10;
    this.amount = 1;
  }
  get total() {
    return this.price * this.amount;
  }
}
decorate(OrderLine, {
  price: observable,
  amount: observable,
  total: computed
});
const orderLine = new OrderLine();
console.log(orderLine.amount, orderLine.price);
console.log(orderLine.total);
console.log(orderLine.amount, orderLine.price);

mobx-babel7.js

function _defineProperty(obj, key, value) { if (key in obj) { Object.defineProperty(obj, key, { value: value, enumerable: true, configurable: true, writable: true }); } else { obj[key] = value; } return obj; }

const {
  observable,
  computed,
  decorate
} = require('mobx');

class OrderLine {
  constructor() {
    _defineProperty(this, "price", 10);
    _defineProperty(this, "amount", 1);
  }
  get total() {
    return this.price * this.amount;
  }
}

decorate(OrderLine, {
  price: observable,
  amount: observable,
  total: computed
});
const orderLine = new OrderLine();
console.log(orderLine.amount, orderLine.price);
console.log(orderLine.total);
console.log(orderLine.amount, orderLine.price);

mobx-source.js

const { observable, computed, decorate } = require('mobx');
class OrderLine {
  price = 10;
  amount = 1;
  get total() { return this.price * this.amount; }
}
decorate(OrderLine, {
  price: observable,
  amount: observable,
  total: computed
})
const orderLine = new OrderLine();
console.log(orderLine.amount, orderLine.price);
console.log(orderLine.total);
console.log(orderLine.amount, orderLine.price);