Flash cards
Review the key moves
What is the main idea behind JS Temporal Differences?
Lesson checks
Practice each idea before moving on
Short Mimo-style checks built from this lesson's code, terms, and sequence.
Which statement best captures the main point of this lesson?
Put the learning moves in the order that makes the concept easiest to apply.
JavaScript since() and until()
The since() method calculates the since duration between two dates.
The until() method calculates the until duration between two dates.
The since() and until() are effectivly the inverse of each other.
All temporal date objects have their own since() method :
- plaindate .since( plaindate )
- plaintime .since( plaintime )
- plainyearmonth .since( plainyearmonth )
- plainmonthday .since( plainmonthday )
- plaindatetime .since( plaindatetime )
- zoneddatetime .since( zoneddatetime )
- instant .since( instant )
All temporal objects have their own until() method :
- plaindate .until( plaindate )
- plaintime .until( plaintime )
- plainyearmonth .until( plainyearmonth )
- plainmonthday .until( plainmonthday )
- plaindatetime .until( plaindatetime )
- zoneddatetime .until( zoneddatetime )
- instant .until( instant )
JavaScript Temporal since()
The since() method calculates the duration between two temporal dates.
Syntax
t1
.since(
t2, options
)Meaning
At time t1 , how much time has passed since time t2 ?
Example
const start = Temporal.PlainDate.from("2026-05-01");
const end = Temporal.PlainDate.from("2026-05-17");
const duration = start.since(end);The since() method returns a Temporal.Duration Object representing the elapsed time.
The duration is positive if the "other" date is in the past .
The duration is negative if the "other" date is in the future .
JavaScript Temporal until()
The until() method calculates the duration between two temporal dates.
Syntax
t1
.until(
t2, options
)Meaning
At time t1 , how much time is it until t2 ?
Example
const start = Temporal.PlainDate.from("2026-05-01");
const end = Temporal.PlainDate.from("2026-05-17");
const duration = start.until(end);Temporal since() vs until()
The methods are opposites.
| Method | Meaning |
|---|---|
| a.since(b) | time from b → a |
| a.until(b) | time from a → b |
Example
const start = Temporal.PlainDate.from("2026-05-01");
const end = Temporal.PlainDate.from("2026-05-17");
const duration1 = start.since(end);
const duration2 = start.until(end);Think
- since = past (since yesterday)
- until = future (until tomorrow)
The Options Parameters
Example
const wedding = Temporal.PlainDate.from("2000-05-17");
const today = Temporal.Now.plainDateISO();
const duration = today.since(wedding);The since() method returns the total number of days, but you can use the largestUnit option to break it down into years and months:
Example
const wedding = Temporal.PlainDate.from("2000-05-17");
const today = Temporal.Now.plainDateISO();
const duration = today.since(wedding, {largestUnit:'years'});PlainTime since()
Example: Plain Time
const start = Temporal.PlainTime.from("09:00");
const end = Temporal.PlainTime.from("17:30");
const duration = end.since(start);ZonedDateTime since()
The since() method calculates the duration between two temporal dates.
Syntax
t1
.since(
t2, options
)Example: ZonedDateTime
const start = Temporal.ZonedDateTime.from( "2026-02-17T09:00:00+01:00[Europe/Oslo]");
const end = Temporal.ZonedDateTime.from( "2026-02-17T17:30:00+01:00[Europe/Oslo]");
const duration = end.since(start);