JavaScript Array sort() Method

What You’ll Learn

The sort() method reorders array elements in place. By default it sorts as strings—which surprises beginners with numbers. This tutorial covers compare functions, ascending/descending order, sorting objects, and safe copy-first patterns.

Introduction

Need names A–Z, prices low-to-high, or scores on a leaderboard? sort() rearranges elements inside the array. It returns the same array reference (now reordered), so you can chain or assign in one expression.

The catch: without a compare function, JavaScript converts each value to a string before comparing. That works for words but often breaks for multi-digit numbers.

Understanding the sort() Method

array.sort(compareFn?) sorts elements in place using UTF-16 string order when no function is provided. With a compare function, you control ordering: return negative if a comes first, zero if equal, positive if b comes first.

Modern JavaScript requires a stable sort: equal elements keep their relative order from before the sort.

📝 Syntax

General form of Array.prototype.sort:

array.sort(compareFn(a, b))

Parameters

• compareFn (optional) — defines sort order. Omitted = string sort.

Return value

• The sorted array (same reference as the original).

Compare function return values

• < 0 — a before b
• 0 — leave order unchanged (stable tie)
• > 0 — a after b

Common patterns

• arr.sort() — default string order.
• arr.sort((a, b) => a - b) — numbers ascending.
• arr.sort((a, b) => b - a) — numbers descending.
• [...arr].sort(fn) — sort a copy, keep original.
• items.sort((a, b) => a.price - b.price) — objects by field.

Examples Gallery

Open DevTools Console (F12) or use Try-it labs. Example N maps to ?tryit=N.

const fruits = ["banana", "apple", "cherry"];

fruits.sort();

console.log(fruits);
// ["apple", "banana", "cherry"]

["apple", "banana", "cherry"]

const nums = [40, 5, 100, 9];

nums.sort();

console.log(nums);
// [100, 40, 5, 9]  ← not numeric order!

[100, 40, 5, 9]

const nums = [40, 5, 100, 9];

nums.sort((a, b) => a - b);

console.log(nums);
// [5, 9, 40, 100]

[5, 9, 40, 100]

const scores = [88, 42, 95, 71];

scores.sort((a, b) => b - a);

console.log(scores);
// [95, 88, 71, 42]

[95, 88, 71, 42]

const products = [
  { name: "Laptop", price: 1200 },
  { name: "Tablet", price: 500 },
  { name: "Phone", price: 800 }
];

products.sort((a, b) => a.price - b.price);

console.log(products.map((p) => p.name + ": $" + p.price).join(", "));
// Tablet: $500, Phone: $800, Laptop: $1200

Tablet: $500, Phone: $800, Laptop: $1200

🚀 Common Use Cases

• Leaderboards — scores high-to-low.
• Product lists — sort by price or rating.
• Names — alphabetical user directories.
• Dates — compare timestamps or Date objects.
• Table UI — column header click sorting.
• Immutable display — [...data].sort(fn) for React state.

📝 Notes

• Mutates the original array.
• Default sort = string UTF-16 order, not numeric.
• Returns the sorted array (same reference).
• Stable sort since ES2019 (equal items keep relative order).
• For immutability: [...arr].sort(fn) or toSorted(fn).
• Undefined and holes behave per spec—avoid sparse arrays when sorting.
• Do not assume a specific algorithm (TimSort-like internally in V8).

💡 Best Practices