stopwatch.js

function Stopwatch() {
  let startTime,
    endTime,
    running,
    duration = 0

  Object.defineProperty(this, 'startTime', {
    get: function () {
      return startTime
    },
  })

  Object.defineProperty(this, 'endTime', {
    get: function () {
      return endTime
    },
  })

  Object.defineProperty(this, 'running', {
    get: function () {
      return running
    },
  })

  Object.defineProperty(this, 'duration', {
    get: function () {
      return duration
    },
    set: function (value) {
      duration = value
    },
  })
}

Stopwatch.prototype.start = function () {
  if (this.running) {
    throw new Error('Stopwatch is already started.')
  }

  this.running = true
  this.startTime = new Date()
}

Stopwatch.prototype.stop = function () {
  if (!this.running) {
    throw new Error('Stopwatch has not started')
  }
  this.running = false
  this.endTime = new Date()

  const seconds = (this.endTime.getTime() - this.startTime.getTime()) / 1000
  this.duration += seconds
}

Stopwatch.prototype.reset = function () {
  this.startTime = null
  this.endTime = null
  this.running = false
  this.duration = 0
}

const sw = new Stopwatch()

//Moving methods to the prototypes to optimize methods but it broke abstraction