SOURCE

class Demo {
    constructor(name, unitPrice, number) {
        this.name = name
        this.unitPrice = unitPrice
        this.number = number
        Demo.count++
    }
    static count = 0

    get totalPrice() {
        return Demo.count * this.number
    }

    increase() {
        this.number++
    }
}

var Demo1 = (() => {
    'use strick'
    function Demo(name, unitPrice, number) {
        if (Object.getPrototypeOf(this) !== Demo.prototype) {
            throw new Error('new')
        }
        this.name = name
        this.unitPrice = unitPrice
        this.number = number
        Demo.count++

        Object.defineProperty(this, 'totalPrice', {
            get() {
                return this.number * Demo.count
            },
            enumerable: false
        })
    }

    Demo.count = 0

    Object.defineProperty(Demo, 'increase', {
        value() {
            if (Object.getPrototypeOf(this) === Demo.prototype.increase.prototype) {
                throw new Error('ddddd')
            }
            return this.number++
        },
        enumerable: false
    })

    return Demo
})()

Object.defineProperty(Demo.prototype, 'totalPrice', {
            get() {
                return this.number * Demo.count
            },
            enumerable: false
        })

var d = new Demo1(1, 2, 3)

console.log(d.totalPrice, 'd.totalPrice')
console.log(d, '<-----d')