Default Sort
sort converts items to strings and sorts lexicographically by default.
This can surprise you with numbers like 10 coming before 2.
JavaScript Tutorial
JavaScript sort()
sort orders array elements in place. Without a compare function it sorts as strings.
For numeric and custom ordering, you should pass a compare function.
Why We Need It
Sorting is common for lists, leaderboards, and UI tables.
Knowing how sort behaves avoids subtle bugs.
Syntax
array.sort()
array.sort((a, b) => a - b)Basic Example
1. Default sort
const nums = [10, 2, 5];
nums.sort();
console.log(nums); // [10, 2, 5] as stringsDefault sort is lexicographic, not numeric.
Real World Example
2. Numeric sort
const nums = [10, 2, 5];
nums.sort((a, b) => a - b);
console.log(nums); // [2, 5, 10]Use a compare function for numeric order.
Multiple Use Cases
Compare Function
Provide a compare function for numeric or custom sorting.
Return a negative number for a before b, positive for a after b, and 0 for equal.
Mutation
sort mutates the original array.
Clone the array first if you need to keep the original.
More Examples
3. Sort objects
const users = [{ age: 30 }, { age: 20 }];
users.sort((a, b) => a.age - b.age);
console.log(users);Compare object fields for custom sorting.
4. Clone before sort
const nums = [3, 1, 2];
const sorted = [...nums].sort((a, b) => a - b);
console.log(nums, sorted);Clone to avoid mutating the original.
Comparison
Without
const nums = [10, 2, 5];
nums.sort();With
const nums = [10, 2, 5];
nums.sort((a, b) => a - b);Common Mistakes and Fixes
Assuming numeric sort
Provide a compare function for numbers.
Mutating original array
Clone before sorting if needed.
Returning boolean in compare
Return negative, zero, or positive numbers.
Interview Questions
Does sort mutate?
Yes, it sorts in place.
How do you sort numbers?
Provide a compare function like (a, b) => a - b.
How do you sort descending?
Use (a, b) => b - a.
Practice Problem
Practice: Sort an array of scores in descending order.
const scores = [20, 5, 30];
// TODO: sort descending
One Possible Solution
const scores = [20, 5, 30];
scores.sort((a, b) => b - a);
console.log(scores);Frequently Asked Questions
Does sort mutate the array?
Yes, sort changes the original array.
Why does sort put 10 before 2?
Default sort compares strings, not numbers.
How do I sort descending?
Use (a, b) => b - a.
Try It Yourself
Try sorting numbers and strings to see differences.