To sort an array of integers in JavaScript, use the sort() method with a custom comparison function to ensure numerical (not lexicographical) sorting. Here’s a detailed guide with examples:
1. Basic Numerical Sorting
By default, sort() treats elements as strings, which can lead to incorrect results for numbers.
Solution: Pass a comparison function to sort().
Ascending Order (Small → Large)
const numbers = [40, 1, 5, 200];
numbers.sort((a, b) => a - b);
console.log(numbers); // [1, 5, 40, 200]Descending Order (Large → Small)
const numbers = [40, 1, 5, 200];
numbers.sort((a, b) => b - a);
console.log(numbers); // [200, 40, 5, 1]2. Why the Comparison Function Matters
Without a comparison function, sort() converts numbers to strings and sorts them lexicographically (alphabetically):
const numbers = [10, 2, 1, 5];
numbers.sort();
console.log(numbers); // [1, 10, 2, 5] (incorrect for numbers!)3. Copying the Array Before Sorting
The sort() method mutates the original array. To avoid this, create a copy first:
const original = [3, 1, 4, 1, 5];
const sorted = [...original].sort((a, b) => a - b);
console.log(original); // [3, 1, 4, 1, 5] (unchanged)
console.log(sorted); // [1, 1, 3, 4, 5]4. Sorting Subranges
Use slice() to sort a subset of the array:
const numbers = [9, 3, 2, 8, 7];
// Sort elements from index 1 to 3
numbers.slice(1, 4).sort((a, b) => a - b);
console.log(numbers); // [9, 2, 3, 8, 7]5. Handling Edge Cases
Negative Numbers
The comparison function works naturally with negatives:
const numbers = [-5, 10, -1, 3];
numbers.sort((a, b) => a - b);
console.log(numbers); // [-5, -1, 3, 10]Large Arrays
Modern JavaScript engines (like V8) use efficient sorting algorithms, so performance is rarely an issue for typical use cases.
Key Takeaways
- Always use
(a, b) => a - bfor ascending order or(a, b) => b - afor descending order. - The
sort()method modifies the original array. Use[...array].sort()to preserve the original. - Lexicographical sorting (default) is not suitable for numbers.
Summary Code
// Ascending order
const sortedAsc = [10, 2, 1, 5].sort((a, b) => a - b);
// Descending order
const sortedDesc = [10, 2, 1, 5].sort((a, b) => b - a);
// Immutable sort
const original = [3, 1, 4];
const sortedCopy = [...original].sort((a, b) => a - b);