Dates and times are one of the most common problems programmers encounter - so why is it that we so often get this space wrong? Let's discuss where our current Date goes bad, better ways to model the date and time space in our code, and how the Temporal proposal making its way through TC39 helps us write correct code for every person in every time zone.

1. PROGRAMMING IN THE 4TH
DIMENSION
MAKING TIME MAKE SENSE
Maggie Johnson-Pint
magpint@Microsoft.com
@maggiepint

2. A day in the life of Maggie.
"Ocean Sunrise" by sombraala is licensed under CC BY-NC-SA
2.0

3. HEY MAGGIE – CAN I HAVE A
MOMENT?
(HA, HA, HA)

4. DID YOU KNOW…
• ABOUT THIS GREAT FALSEHOODS PROGRAMMERS BELIEVE ABOUT TIME VIDEO?
• THE PLACES WHERE MIDNIGHT DOESN’T EXIST?
• LEAP YEAR 2012 BRICKED EVERY ZUNE FOR A DAY?
• WE MIGHT COLONIZE MARS SOON? WE’LL NEED TIME THERE TOO!
• THERE’S SOME COUNTRY SOMEWHERE WHERE A WHOLE DAY IS MISSING DUE TO A TIME ZONE
CHANGE?
• THERE IS A GAP BETWEEN THE JULIAN AND GREGORIAN CALENDARDS?

5. YES. YES I DO.
"Soi dog - Bangkok" by ashabot is licensed under CC BY-NC-SA

6. AS PROGRAMMERS, WE OFTEN THINK ABOUT DATE AND TIME
PROBLEMS AS A SORT OF “FUN TRIVIA”.

7. GETTING THIS STUFF RIGHT MATTERS.
• DATE AND TIME PROBLEMS ARE PRIMARY APPLICATIONS IN COMPUTING
• GETTING THESE PROBLEMS WRONG PROFOUNDLY AFFECTS IMPORTANT STUFF
• PEOPLE GETTING PLACES ON TIME
• PAYCHECKS HAVING THE RIGHT AMOUNT OF MONEY
• COORDINATING INTERNATIONAL CONFERENCE CALLS
• MEDICAL DEVICE BEHAVIOR
• POOR PRACTICES IN DATE TIME PROGRAMMING DISPROPORTIONATELY AFFECT
• NON-ENGLISH SPEAKING PEOPLE
• HOURLY WAGE WORKERS
• PEOPLE IN OTHER TIME ZONES

8. MEET THE WORST SOLUTION POSSIBLE.
new Date();
ate()

9. DATE HAS A LOT OF
PROBLEMS

10. MONTHS INDEX FROM ZERO?
let a = new Date(2019,12,3);
console.log(a.toISOString()); //2020-01-03T06:00:00.000Z

11. MUTABILITY
function addDays(date, days) {
date.setDate(date.getDay() + days)
return date;
}
let a = new Date('2019-12-03');
let b = addDays(a, 3);
console.log(a.toISOString()) // 2019-12-05T00:00:00.000Z
console.log(b.toISOString()) // 2019-12-05T00:00:00.000Z

12. TIME ZONE GAPS
I NEED TO MEET WITH THE SAN FRANCISCO OFFICE AT 9:00 THEIR TIME NEXT WEEK. WHAT TIME IS IT HERE?
NO IDEA.
console.log(new Date().toString())
// Tue Dec 03 2019 16:03:27 GMT-0600 (Central Standard Time)
console.log(new Date().toISOString())
// 2019-12-03T22:03:27.533Z

13. NO DATE-ONLY REPRESENTATION
let sulusBirthday = new Date('2014-09-12');
console.log(sulusBirthday.toDateString()); // Thu Sep 11 2014

14. INEXPLICABLE PARSE BEHAVIORS
let sulusBirthday = new Date('2014-09-12');
console.log(sulusBirthday.toISOString());
// 2014-09-12T00:00:00.000Z
let sulusBirthdayAtMidnight = new Date('2014-09-12T00:00:00')
console.log(sulusBirthdayAtMidnight.toISOString());
// 2014-09-12T07:00:00.000Z

15. SULU IS MY
DOG
HE’S VERY CUTE

17. “
”
A DOMAIN MODEL IS A SYSTEM OF
ABSTRACTIONS THAT DESCRIBES SELECTED
ASPECTS OF A SPHERE OF KNOWLEDGE,
INFLUENCE OR ACTIVITY
ERIC EVANS – DOMAIN DRIVEN DESIGN
WHAT IS A DOMAIN MODEL?

18. THE TEMPORAL PROPOSAL IN TC39
PROVIDES A COMPLETE DOMAIN MODEL

19. TEMPORAL WILL BE A
NEW GLOBAL
PENDING WEB COMPATIBILITY TESTING
new Temporal.Date(2020,01,01);
new Temporal.Absolute(1574074321816000000n);

20. NEW TYPES
• TEMPORAL.ABSOLUTE
• TEMPORAL.DATETIME
• TEMPORAL.DATE
• TEMPORAL.TIME
• TEMPORAL.TIMEZONE
• TEMPORAL.DURATION
• TEMPORAL.YEARMONTH
• TEMPORAL.MONTHDAY

21. ABSOLUTE
Date()
Absolute Time
(Temporal.Absolute)

22. THE GLOBAL TIMELINE
1 2 3 4 5 6 7 8 9
Point in absolute time

23. ABSOLUTE SCENARIOS
• LOG DATA
• POINT-IN-TIME EVENTS

24. TEMPORAL.ABSOLUTE()
new Temporal.Absolute(epochNanoSeconds : bigint)
const date = new Temporal.Absolute(1574074321816000000n);
date.toString(); // 2019-11-18T10:52:01.816Z
Temporal.Absolute.from(thing: string | object)
const date = Temporal.Absolute.from("2019-11-18T11:00:00.000Z");
date.toString(); // 2019-11-18T11:00Z

25. DATETIME
Date()
Absolute Time
(Temporal.Absolute)
Local Date and Time
(Temporal.DateTime)

26. LOCAL TIME
TEMPORAL.DATETIME
• A LOCAL TIME IS A PERSPECTIVE OF TIME
• IT DOES NOT REPRESENT A POINT ON THE
GLOBAL TIMELINE
• IT OFTEN NOT A CONTIGUOUS TIMELINE
(DST, TIME ZONE SHIFTS)

27. DATETIME SCENARIOS
• DATES AND TIMES ON NON-CONNECTED DEVICES LIKE WATCHES, FITBITS, TIME CLOCKS OR
INSULIN PUMPS

28. USING DATETIME
let timeFromDeviceString = '2019-12-05T08:12:03.001';
let localDateTime = Temporal.DateTime.from(timeFromDeviceString);

29. TIMEZONE
Date()
Absolute Time
(Temporal.Absolute)
Local Date and Time
(Temporal.DateTime)
Temporal.TimeZone

30. TEMPORAL.TIMEZONE
• REPRESENTS ONE OF:
• UTC
• FIXED OFFSET (+01:00)
• IANA TIME ZONE (EUROPE/PARIS)
• KEEP IN MIND – AN IANA TIME ZONE IS A COLLECTION OF HISTORICAL OFFSETS OVER TIME
• WHEN COMBINED WITH AN ABSOLUTE OR A DATETIME, PRESENTS A COMPLETE PICTURE OF A
POINT IN TIME
• DATE AND TIME, LOCAL AND UTC

31. WHAT POINT IN TIME DID THIS INSULIN PUMP RUN
AT?
let timeFromDeviceString = '2019-12-05T08:12:03.001';
let userProvidedTz = 'Europe/Paris';
let localDateTime = Temporal.DateTime.from(timeFromDeviceString);
let timeZone = new Temporal.TimeZone(userProvidedTz);
let globalTime = timeZone.getAbsoluteFor(localDateTime);

32. DATE
Date()
Absolute Time
(Temporal.Absolute)
Local Date and Time
(Temporal.DateTime)
Temporal.TimeZone
Date Only
(Temporal.Date)

33. TEMPORAL.DATE
• REPRESENTS A DATE WITHOUT A TIME
• PREVENTS ‘TIME ASSUMPTION’ ERRORS THAT CAUSE UNEXPECTED BEHAVIOR
• SCENARIOS:
• DATES OF BIRTH
• EMPLOYMENT HIRING DATES
• HOLIDAYS
• REPORT GROUPINGS
• “FOR THE BUSINESS DAY OF”

34. SULU’S BIRTHDAY – MADE BETTER
let birthday = Temporal.Date.from(‘2014-09-12');
console.log(birthday.toString()) //2014-09-12
let birthdayLong = Temporal.Date.from(‘2014-09-12T00:00:00.000');
console.log(birthdayLong.toString()) //2014-09-12
console.log(birthdayLong.day) // 12
console.log(birthdayLong.hour) // undefined

35. TIME
Date()
Absolute Time
(Temporal.Absolute)
Local Date and Time
(Temporal.DateTime)
Temporal.TimeZone
Date Only
(Temporal.Date)
Time Only
(Temporal.Time)

36. TEMPORAL.TIME
• REPRESENTS A TIME WITHOUT A DATE
• PREVENTS ‘DATE ASSUMPTION’ ERRORS THAT CAUSE UNEXPECTED BEHAVIOR
• SCENARIOS:
• RECURRING MEETING SCHEDULES
• DATA FROM NON-CONNECTED CLOCKS

37. FINDING UTC POINT-IN-TIME OF RECURRING
MEETING
let meeting1 = Temporal.Date.from('2020-01-01');
let meeting2 = Temporal.Date.from('2020-04-01');
let time = Temporal.Time.from('10:00:00');
let timeZone = new Temporal.TimeZone('Europe/Paris');
let absolute1 = timeZone.getAbsoluteFor(meeting1.withTime(time));
// 2020-01-01T09:00:00.000Z
let absolute2 = timeZone.getAbsoluteFor(meeting2.withTime(time));
// 2020-04-01T08:00:00.000Z
ProTip: Store recurring meeting times in local
and convert

38. DURATION
Date()
Absolute Time
(Temporal.Absolute)
Local Date and Time
(Temporal.DateTime)
Temporal.TimeZone
Date Only
(Temporal.Date)
Time Only
(Temporal.Time)
Duration
(Temporal.Duration)

39. TEMPORAL.DURATION
• USED TO EXPRESS LENGTHS OF TIME
• USEFUL TO FORMAT IN AND OF ITSELF
• “SHE WON THE RACE WITH A TIME OF 00:05:25.122”
• USED TO ADD AND SUBTRACT AMOUNTS OF TIME FROM ABSOLUTE, DATETIME, DATE, TIME
• RETURN VALUE OF A DIFFERENCE FUNCTION BETWEEN TWO ABSOLUTES OR DATES OR TIMES

40. EXACTLY HOW OLD IS MR SULU?
let birthday = Temporal.Date.from('2014-09-12');
let age = Temporal.getDate().difference(birthday);
// P5Y2M3W4D

41. OTHER GOOD STUFF
SO MUCH CONTENT, SO LITTLE TIME

42. YEAR/MONTH AND MONTH/DAY
• YEARMONTH IS USED TO REPRESENT REPORTING PERIODS, HISTORICAL TIMEFRAMES, ETC
• DECEMBER OF 2019
• MONTHDAY IS USED TO REPRESENT RECURRING DATES LIKE HOLIDAYS OR BIRTHDAYS
• MR SULU’S BIRTHDAY IS SEPTEBMBER 12
• NEW YEAR’S DAY IS JANUARY 1

43. ALTERNATE CALENDARS
• TC39 IS WORKING ON WAYS TO SUPPORT ALTERNATE CALENDAR SYSTEMS LIKE:
• HEBREW
• HIJRI
• JAPANESE
• AND MANY MORE
• THIS DISCUSSION IS VERY EARLY AND YOUR FEEDBACK WOULD BE VERY HELPFUL
• IF YOU USE A CALENDAR SYSTEM OTHER THAN GREGORIAN REGULARLY, WHEN AND HOW?
• HTTPS://GITHUB.COM/TC39/PROPOSAL-TEMPORAL/ISSUES/268

44. HOW DO WE GET THIS DONE?
STANDARDS AND THEIR PROCESSES

45. TEMPORAL IS
CURRENTLY
AT STAGE 2
• TC39 HAS A 4-STAGE PROCESS FOR MOVING PROPOSALS
FORWARD
• WHEN TEMPORAL REACHES STAGE 3, ENGINES WILL PICK IT
UP FOR A TEST IMPLEMENTATION
• UNTIL STAGE 3, APIS ARE INCREDIBLY UNSTABLE
• GOOD NEWS – AT A TOP LEVEL EVERYONE WANTS IT

46. CONTRIBUTING
• WE WELCOME CONTRIBUTIONS TO THE TEMPORAL SPECIFICATION AND POLYFILL
• YOU CAN FIND IT AT HTTPS://GITHUB.COM/TC39/PROPOSAL-TEMPORAL
• THE POLYFILL IS IN THIS REPO – CHECK IT OUT!
• WE WILL PUBLISH WHEN API IS STABLE

47. THANK YOU TO INCREDIBLE PEOPLE
• PHILIPP DUNKEL (BLOOMBERG)
• MATT JOHNSON-PINT (MICROSOFT)
• DANIEL EHRENBERG (IGALIA)
• RICHARD GIBSON (ORACLE)
• SHANE CARR (GOOGLE)
• BRIAN TERLSON (MICROSOFT)
• UJJWAL SHARMA (IGALIA)
• MS2GER (IGALIA)

48. MAGGIE JOHNSON-PINT
MAGPINT@MICROSOFT.COM
@MAGGIEPINT
HTTPS://GITHUB.COM/TC39/PROPOSAL-TEMPORAL