Add methods to the Date class to allow incrementing and decrementing dates

increment-dates.js

var types = [
  'Date',
  'FullYear',
  'Hours',
  'Milliseconds',
  'Minutes',
  'Month',
  'Seconds',
  'UTCDate',
  'UTCFullYear',
  'UTCHours',
  'UTCMilliseconds',
  'UTCMinutes',
  'UTCMonth',
  'UTCSeconds'
]

types.forEach(function (type) {
  Date.prototype['increment' + type] = function (amount) {
    this['set' + type](this['get' + type]() + amount)

    return this
  }

  Date.prototype['decrement' + type] = function (amount) {
    this['set' + type](this['get' + type]() - amount)

    return this
  }
})

var foo = new Date()
foo.incrementMinutes(42)
foo.decrementHours(20)