date.js

'use strict'
var monthCount = 12

var normalDaySpec = [
  31, // January
  28, // February
  31, // March
  30, // April
  31, // May
  30, // June
  31, // July
  31, // August
  30, // September
  31, // October
  30, // November
  31 // December
]
var leapDaySpec = [
  31, // January
  29, // February
  31, // March
  30, // April
  31, // May
  30, // June
  31, // July
  31, // August
  30, // September
  31, // October
  30, // November
  31 // December
]

// provide a year-specific day spec
function daySpec (year) {
  return ((year % 400 === 0 || (year % 4 === 0 && year % 100 !== 0)) ? leapDaySpec : normalDaySpec)
}
/* eslint-disable no-extend-native */
Date.prototype.addYear = function () {
  this.setFullYear(this.getFullYear() + 1)
}

Date.prototype.addMonth = function () {
  var m = this.getMonth() + 1
  if (m === monthCount) {
    m = 0
    this.addYear()
  }

  this.setMonth(m)
}

Date.prototype.addDay = function () {
  var spec = daySpec(this.getFullYear())
  var d = this.getDate() + 1

  if (d > spec[this.getMonth()]) {
    d = 1

    this.setDate(d)
    this.addMonth()
  }

  this.setDate(d)
}

Date.prototype.addHour = function () {
  var h = this.getHours() + 1

  if (h === 24) {
    h = 0
    this.addDay()
  }

  this.setHours(h)
}

Date.prototype.addMinute = function () {
  var m = this.getMinutes() + 1

  if (m === 60) {
    m = 0
    this.addHour()
  }

  this.setMinutes(m)
}

Date.prototype.addSecond = function () {
  var s = this.getSeconds() + 1

  if (s === 60) {
    s = 0
    this.addMinute()
  }

  this.setSeconds(s)
}

Date.prototype.substractYear = function () {
  this.setFullYear(this.getFullYear() - 1)
}

Date.prototype.substractMonth = function () {
  var m = this.getMonth() - 1
  if (m < 0) {
    m = 0
    this.substractYear()
  }

  this.setMonth(m)
}

Date.prototype.substractDay = function () {
  // var spec = daySpec(this.getFullYear())
  var d = this.getDate() - 1

  // if (d > spec[this.getMonth()]) {
  //   d = 1
  //   this.setDate(d)
  //   this.substractMonth()
  // }

  this.setDate(d)
}

Date.prototype.substractHour = function () {
  var h = this.getHours() - 1

  if (h < 0) {
    h = 0
    this.substractDay()
  }

  this.setHours(h)
}

Date.prototype.substractMinute = function () {
  var m = this.getMinutes() - 1

  if (m < 0) {
    m = 59
    this.substractHour()
  }

  this.setMinutes(m)
}

Date.prototype.substractSecond = function () {
  var s = this.getSeconds() - 1
  if (s < 0) {
    s = 59
    this.substractMinute()
  }
  this.setSeconds(s)
}