Use a comparator that subtracts date timestamps. For an array of objects with Date values, this sorts oldest first without changing the original array:
interface Event {
title: string;
date: Date;
}
const ascending = [...events].sort(
(a, b) => a.date.getTime() - b.date.getTime(),
);
const descending = [...events].sort(
(a, b) => b.date.getTime() - a.date.getTime(),
);Use the ascending comparator for oldest first and the descending one for newest first. The spread copies the array before JavaScript’s in-place sort() runs.
Sort Date objects by timestamp
A JavaScript Date represents a timestamp in milliseconds since the Unix epoch. Calling getTime() on two dates and subtracting the results gives the numeric comparison sort() needs. The same pattern works for a plain array of dates:
const dates: Date[] = [new Date("2025-04-10"), new Date("2023-08-01")];
const oldestFirst = [...dates].sort(
(a, b) => a.getTime() - b.getTime(),
);A negative comparator result places the first item before the second; a positive result places it after. A zero result means the comparator considers them equal. Avoid the default sort() with no comparator: it converts values to strings and sorts their text, which is not chronological date ordering. See MDN’s Array.prototype.sort() reference and MDN’s Date reference.
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Choose whether to mutate the input
Array.prototype.sort() changes the array it is called on and returns that same array. In the examples, [...events] makes a shallow copy first, so the original array order stays intact. The objects inside the copied array are still shared; sorting does not clone or alter their date values.
- Keep the original array order: use
[...events].sort(compareDates). - Sort the existing array in place: use
events.sort(compareDates)when changing its order is intended. - Use
toSorted(): MDN documents this non-mutating alternative, but check that the project’s runtime and TypeScript library target support it before relying on it.
Handle date strings as input data
If dates arrive as strings, first establish their format and what their time zone means. The standard date-time string format is the portable choice; parsing other human-readable formats can be implementation-specific, and some strings are interpreted in local time. For values representing instants, use UTC (Z) or an explicit offset. See MDN’s Date() constructor reference.
Rank #2
- TypeScript implements a superset of syntax for strictly typed development, facilitating deep static analysis and enhanced development environment integration. The compiler translates source into standard script formats, ensuring parity across any runtime.
- TypeScript is ideal for front-end developers, full-stack engineers, and software architects who build large-scale web applications. It serves those looking to improve code excellence, reduce bugs through static checking, and maintain complex projects more.
- Lightweight, Classic fit, Double-needle sleeve and bottom hem
For example, validate and parse strings before sorting. This version rejects an invalid value when it is encountered:
function timestamp(value: string): number {
const result = Date.parse(value);
if (Number.isNaN(result)) {
throw new Error(`Invalid date: ${value}`);
}
return result;
}
const sorted = [...rows].sort(
(a, b) => timestamp(a.date) - timestamp(b.date),
);For repeated comparisons, parse each string once when data enters the application and store its timestamp, rather than parsing inside the comparator. This avoids repeating work during sorting; it is an implementation recommendation, not a benchmark claim.
Do these 3 things before closing this tab:
1Clear out junk files and repair common Windows errors2Fix the driver behind crashes, sound loss and screen glitches3Repair Windows errors before they cause bigger problemsIf a value represents a calendar day rather than a precise instant, decide how calendar-day ordering should work before converting it to a timestamp. Turning local dates into instants without an explicit rule can make the displayed day shift across time zones.
Define what happens to invalid dates and ties
An invalid Date has a NaN timestamp. Subtracting that value does not produce a normal chronological comparison, so validate dates before sorting and choose a policy: reject them, filter them out, or explicitly place them last. Calling toISOString() on an invalid date throws a RangeError; see MDN’s invalid-date error reference.
JavaScript sorting is stable in ECMAScript 2019 and later: items the comparator considers equal retain their original relative order. If equal timestamps need a secondary order, add a tie-breaker, such as an ID or title. Comparators should be consistent and return a three-way result; a boolean comparator such as (a, b) => a.date > b.date does not express before, after, and equal correctly and can lead to engine-dependent results.
const sortedByDateThenTitle = [...events].sort((a, b) => {
const byDate = a.date.getTime() - b.date.getTime();
return byDate || a.title.localeCompare(b.title);
});Which version should you use?
| Situation | Operation | What to know |
|---|---|---|
Plain Date[], oldest first |
dates.sort((a, b) => a.getTime() - b.getTime()) |
Mutates dates. |
| Objects with dates, newest first | items.sort((a, b) => b.date.getTime() - a.date.getTime()) |
Reverse the subtraction to reverse the order. |
| Preserve the source array | [...items].sort(compareDates) |
Copies the array, not the objects inside it. |
| String dates | Validate and parse, then compare timestamps | Use a known format and an explicit time-zone policy. |
What TypeScript changes—and what it does not
The ordering behavior comes from JavaScript’s built-in Array.prototype.sort() and Date; TypeScript adds static type checking. Comparing getTime() results makes the numeric operation explicit and avoids relying on arithmetic directly between Date objects. For a basic coding example, no extra date-sorting library is needed.
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