Sorting in JavaScript

Written by Swapnil RajaPublished 28 Aug 2026

You will almost never write a sorting algorithm at work. You will constantly write comparators - and getting one wrong is a bug that survives review because the output looks nearly right.

The default is wrong for numbers

The bug everyone hits once

javascript

const nums = [10, 9, 100, 1]

nums.sort()
console.log(nums)   // [1, 10, 100, 9]  — sorted as strings

nums.sort((a, b) => a - b)
console.log(nums)   // [1, 9, 10, 100]  — correct

PreviousClassic Backtracking Problems NextSorting Algorithms You Should Know

Comparators you will actually write

javascript

const items = [10, 2, 33, 4]
const names = ["Zoe", "ada", "Bob"]
const users = [
  { name: "Ada", age: 36 },
  { name: "Bob", age: 36 },
  { name: "Cy", age: 21 },
]
const posts = [{ published: "2024-01-02" }, { published: "2023-05-01" }]

// Numbers, ascending and descending.
items.sort((a, b) => a - b)
items.sort((a, b) => b - a)

// Strings, respecting accents and locale.
names.sort((a, b) => a.localeCompare(b))

// By a field.
users.sort((a, b) => a.age - b.age)

// By one field, then another as a tiebreak.
users.sort((a, b) => a.age - b.age || a.name.localeCompare(b.name))

// Dates.
posts.sort((a, b) => new Date(b.published) - new Date(a.published))

Sorting without mutating

javascript

const original = [3, 1, 2]

const sorted = [...original].sort((a, b) => a - b)
// or, in newer runtimes:
const sorted2 = original.toSorted((a, b) => a - b)

console.log(original)  // [3, 1, 2] — untouched

Precompute instead of recomputing

javascript

const posts = [
  { date: "2024-03-01" },
  { date: "2023-01-15" },
  { date: "2024-01-02" },
]

// Slow — parses dates on every comparison.
posts.sort((a, b) => new Date(a.date) - new Date(b.date))

// Fast — parse once, then sort by the number.
const withTime = posts.map((p) => ({ post: p, time: new Date(p.date).getTime() }))
withTime.sort((a, b) => a.time - b.time)
const sorted = withTime.map((x) => x.post)

Sorting in JavaScript

The default is wrong for numbers

How a comparator works

sort mutates

Stability, and why it matters

What it costs