JS Temporal Differences
Calculate Temporal Differences
You calculate the differnce between two temporal dates using until() or since().
The since() method is effectively the inverse of the
until() method.
Or the until() method is the inverse of the
since() method.
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: Plain Date
const start = Temporal.PlainDate.from("2026-05-01");
const end = Temporal.PlainDate.from("2026-05-17");
const duration = end.since(start);
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Example: Plain Time
const start = Temporal.PlainTime.from("09:00");
const end = Temporal.PlainTime.from("17:30");
const duration = end.since(start);
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The Options Parameters
Example
const wedding = Temporal.PlainDate.from('2000-05-17');
const today = Temporal.Now.plainDateISO();
const duration = today.since(wedding);
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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('2026-05-17');
const today = Temporal.Now.plainDateISO();
const duration = today.since(wedding, {largestUnit:'years'});
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JavaScript Temporal until()
The until() method calculates the duration between two temporal dates.
The until() method is effectively the inverse of the
since() method.
Syntax
t1.until(t2, options)
Meaning:
At time t1, how much time is it until t2?
Example
Return a Duration representing the time between two dates:
const start = Temporal.PlainDate.from("2026-05-01");
const end = Temporal.PlainDate.from("2026-05-17");
const duration = start.until(end);
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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 = end.since(start);
const duration2 = start.until(end);
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Both return the same duration.
Think:
- since = past
- Until = future
Examples:
- since yesterday
- until tomorrow
The compare() Method
The compare() method returns -1 if the first date is earlier, 1 if it is later, and 0 if they are equal:
Example
// Create two Temporal objects
const date1 = Temporal.PlainDate.from("2026-05-17");
const date2 = Temporal.PlainDate.from("2024-12-25");
// Compare the dates
result = Temporal.PlainDate.compare(date1, date2);
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The compare() method is designed to be passed directly into the JavaScript Array.sort() method:
Example
// Create an Array of dates
const dates = [
Temporal.PlainDate.from("2026-05-17"),
Temporal.PlainDate.from("2022-01-01"),
Temporal.PlainDate.from("2024-12-25")
];
// Sort chronologically
dates.sort(Temporal.PlainDate.compare);
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Date Comparison
Always use the equals() or compare() methods rather than standard equality operators.
The equals() Method
Example
// Create two Temporal objects
const date1 = Temporal.PlainDate.from('2026-05-17');
const date2 = Temporal.PlainDate.from('2026-05-17');
let result = date1.equals(date2);
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