DSL for expressing and comparing dates and times

Usage no npm install needed!

<script type="module">
  import anHourAgo from '';



an.hour.ago is a small utility which enables wonderfully expressive date and time manipulation in JavaScript.

Before we proceed, let me be clear that if supporting Internet Explorer is a requirement, you'd best turn back now. If, on the other hand, you're writing server-side JavaScript (or CoffeeScript) and desire an elegant means of expressing relative dates and times, read on!

Let's start with a simple example...

# CoffeeScript                                  # JavaScript
3.days.ago                                      # 3..days.ago

This produces a Date instance representing 72 hours before the present. Neat. What about the future?

1.minute.from_now                               # 1..minute.from_now

Easy! Note the use of minute rather than minutes. The two are synonymous; singular and plural properties exist for each of the supported units.

Decimals? You betcha:

1.5.hours.ago                                   # 1.5.hours.ago

In fact, the JavaScript is identical to the CoffeeScript in this case as the awkward double dot is not required.

What about dates relative to other points in time?

tomorrow  =                      # var tomorrow  =
halloween = new Date '31 October 2011'          # var halloween = new Date('31 October 2011')
christmas = new Date '25 December 2011'         # var christmas = new Date('25 December 2011')
1.week.from tomorrow                            # 1..week.from(tomorrow)
2.days.after halloween                          # 2..days.after(halloween)
1.week.before christmas                         # 1..week.before(christmas)

from and after are synonymous; use whichever reads better.

This is pleasing, you may be thinking, but I'd never say “one week from tomorrow” – it sounds a bit stiff.

Well, if you must...

a = an = 1                                      # var a = 1, an = 1
a.week.from tomorrow                            # a.week.from(tomorrow)
a.fortnight.from_now                            # a.fortnight.from_now
an.hour.ago                                     # an.hour.ago

Oh, and I should mention, you can add NaturalDate instances using the and method:

an.hour.and(58.minutes).from_now                # an.hour.and(58..minutes).from_now
11.hours.and(36.minutes).and(9.seconds).ago     # 11..hours.and(36..minutes).and(9..seconds).ago

Can you help me with date comparison? To determine whether an event occurred more than a week ago I have to ask whether its numeric representation is less than that of "a week ago". It makes my head hurt.

Perhaps you find this more natural?


A practical example:

user_registered = db.get(id).registration_date

$('#tips').show() if user_registered.less_than(15.minutes).ago

before/after can follow less_than/more_than:

apply_late_fee() if costume_returned.more_than(2.days).after halloween

There's also an either_side_of method which does what it says on the tin:

unfortunate = birthday.less_than(3.days).either_side_of christmas

That just about covers it.

Running the test suite

make setup
make test

One last thing...

To be clear, an.hour.ago fiddles with Date.prototype and Number.prototype. Two properties are added to Date.prototype:

  • less_than
  • more_than

The following properties are added to Number.prototype:

  • day
  • days
  • hour
  • hours
  • millisecond
  • milliseconds
  • minute
  • minutes
  • second
  • seconds
  • week
  • weeks

Each of these properties has a "getter" which returns a NaturalDate object. The rest of the methods (before, after/from, and and) are attached to NaturalDate.prototype (which is not exposed).