sort() is one of the most misused array methods in JavaScript: it mutates the original array in place, and its default comparator converts everything to strings — silently breaking numeric sorts unless you supply your own comparator.
1Array.prototype.sort() | JavaScript Tutorial - In-Depth Guide Part 1
sort() mutates the array in place and also returns it — a rare case among modern array methods of both mutating and returning.
const nums = [3, 1, 2];
const sorted = nums.sort();
sorted === nums; // true — same array, mutated in placeMutates In Place
2Array.prototype.sort() | JavaScript Tutorial - In-Depth Guide Part 2
Without a comparator, sort() converts every element to a string and compares them alphabetically — which breaks numeric ordering.
[10, 1, 2].sort(); // [1, 10, 2] — alphabetical, not numeric!The Default Is Alphabetical
3Array.prototype.sort() | JavaScript Tutorial - In-Depth Guide Part 3
A comparator function fixes this: return a negative number if a should come first, positive if b should, or zero if they're equal.
[10, 1, 2].sort((a, b) => a - b); // [1, 2, 10] — correctThe Comparator Function
4Array.prototype.sort() | JavaScript Tutorial - In-Depth Guide Part 4
Sorting an array of objects by a property requires comparing that specific property inside the comparator.
users.sort((a, b) => a.age - b.age);
names.sort((a, b) => a.localeCompare(b));Sorting by Property
5Array.prototype.sort() | JavaScript Tutorial - In-Depth Guide Part 5
Modern JavaScript engines guarantee sort() is stable — elements that compare as equal retain their original relative order.
// Elements with equal keys keep their relative order:
people.sort((a, b) => a.lastName.localeCompare(b.lastName));Stable Sort Guarantee
6Step-by-Step Breakdown
sort() mutates the array in place and also returns it — a rare case among modern array methods of both mutating and returning.
Checkpoint: After calling arr.sort(), is the original arr variable's array mutated?
- →Yes, sort() mutates the array in place
- →No, it always returns a new array
Without a comparator, sort() converts every element to a string and compares them alphabetically — which breaks numeric ordering.
Checkpoint: What does [10, 1, 2].sort() (no comparator) return?
- →[1, 10, 2], sorted alphabetically as strings
- →[1, 2, 10], sorted numerically
A comparator function fixes this: return a negative number if a should come first, positive if b should, or zero if they're equal.
Sorting an array of objects by a property requires comparing that specific property inside the comparator.
Modern JavaScript engines guarantee sort() is stable — elements that compare as equal retain their original relative order.
Next, we'll explore 'Immutable Sorting with toSorted()'.
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Advanced cheat sheets, SEO tricks, and interview prep for this topic.
Browser Support
Fully supported.
Fully supported.
Fully supported.
Fully supported.
Accessibility (A11y)
1Announce Sort Order Changes to Assistive Technology
When a user changes a sortable table's sort column or direction, update the corresponding column header's aria-sort attribute (ascending/descending/none) so screen reader users are informed of the current sort state.
SEO Implications
- 1
Consistent Sort Order Improves Perceived Content Stability
Using a stable, well-defined sort for listing pages (like product or article listings) avoids items appearing to reshuffle unpredictably between visits, which can affect user trust signals even though sort order itself is not a direct ranking factor.
Best Practices
Always Provide a Comparator When Sorting Numbers
The default string-based comparison silently produces wrong results for numeric data, so `(a, b) => a - b` (or `b - a` for descending) should be considered mandatory for numeric sorts.
Copy the Array First If the Original Order Must Be Preserved
Since sort() mutates in place, use `[...arr].sort(...)` (or toSorted()) whenever other code still needs the array in its original order.
Frequent Bugs
Sorting an array of numbers without a comparator, silently producing an alphabetically-sorted (and numerically wrong) result.
Always supply an explicit numeric comparator, e.g. `(a, b) => a - b`, whenever sorting numbers.
Calling `.sort()` on an array that's also referenced elsewhere in the app (like shared state), unexpectedly mutating that shared reference and causing bugs in unrelated code.
Copy the array first with spread (`[...arr].sort(...)`) or use the newer, non-mutating toSorted() method when the original order must be preserved for other consumers.
Real-World Examples
Sorting a Product List by Price, Then by Name
An e-commerce listing needed to sort products by ascending price, with same-priced items ordered alphabetically by name using the sort's stability guarantee.
const sorted = [...products]
.sort((a, b) => a.name.localeCompare(b.name))
.sort((a, b) => a.price - b.price);
// Stable sort means the name-sort survives as the tiebreaker