Numeric ascending order
Ordering numeric data such as scores, prices, or timestamps with (a, b) => a - b.
JavaScript · Function
sort
Array.prototype.sort() sorts an array in place and returns the same array. By default it compares string representations in UTF-16 order; pass a comparator for custom ordering.
How it works
sort() rearranges an array's existing elements in place and returns that same array. With no comparator, it compares string representations in UTF-16 code-unit order; with a comparator, its numeric result determines which element comes first.
Syntax
sort()
sort(compareFn)Parameters
| Name | Type | Description |
|---|---|---|
compareFn | function | Optional function receiving two elements and returning a number that determines their relative order. |
Returns
The reference to the original array, now sorted.
Key points
- The method rearranges the existing array and returns that identical array object.
- Leaving out the comparator triggers string conversion before comparison.
- Default ordering follows character code-point values rather than numeric magnitude.
- Return a negative comparator result to place the first argument before the second.
- Return a positive comparator result to place the first argument after the second.
- A zero or NaN comparator result treats the compared elements as equal in ordering.
Common mistakes
- Without a comparator, numeric-looking values are sorted lexicographically rather than by numeric value.
- The comparator is not invoked for undefined elements, and those elements always move to the end.
- Do not rely on a particular sorting algorithm or complexity because implementations may differ.
- Use
toSorted()instead when preserving the original array is required.
Example: Sort numbers numerically
const scores = [10, 2, 30];
scores.sort((a, b) => a - b);
console.log(scores); // [2, 10, 30]Provide a numeric comparator when sorting numbers so their values determine ascending order.
When to use it
Sort objects by a property
Arranging records by a selected field with a comparator that compares the field values.
Locale-aware text order
Ordering text according to a locale by supplying a comparator such as one produced by Intl.Collator.
Interview questions
QDoes sort() mutate the original array?
sort() mutates the array and returns a reference to that same, now-sorted array. It does not create a separate array.
Follow-up: How would you sort without mutation? Use toSorted(), which returns a sorted copy while leaving the source array unchanged.
QWhat ordering does sort() use by default?
Without compareFn, elements are converted to strings and compared in UTF-16 code-unit order. Therefore, the default behavior is not numeric ordering for ordinary arrays.
Follow-up: How do you sort numbers ascending? Pass (a, b) => a - b as the comparator.
QHow does compareFn control ordering?
A comparator receives two defined elements, a and b. A negative result places a first, a positive result places b first, and zero or NaN treats them as equal.
Follow-up: What happens to undefined elements? They are placed at the end without calling the comparator for them.
Related
Array.prototype.toSorted()Array.prototype.reverse()Intl.Collator