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How to Sort a Set in JavaScript

A Set in JavaScript is a collection of unique values, but a key characteristic is that it maintains insertion order, not sorted order. This means that if you need to display or process the items in a Set in a sorted fashion (e.g., alphabetically or numerically), you must first convert it to an array, sort the array, and then optionally convert it back to a Set.

This guide will teach you the standard and most modern method for sorting a Set by converting it to an Array using the spread syntax (...). You will learn how to sort both strings and numbers correctly.

The Core Problem: Sets Are Not Self-Sorting​

A Set is optimized for fast lookups and ensuring uniqueness. It remembers the order in which elements were added, but it does not have a built-in .sort() method like an Array.

Example of code with problems: the order is based on insertion but we want the order based on value!

// Problem: The order of this Set is based on insertion, not value.
const mySet = new Set();
mySet.add('cherry');
mySet.add('apple');
mySet.add('banana');

// Iterating over the Set gives the insertion order
for (const item of mySet) {
  console.log(item);
}

Output:

cherry
apple
banana

To get a sorted result, we must use the sorting capabilities of an Array.

Solution: Convert to Array, Sort, and Convert Back​

The process is a simple, three-step chain:

  1. Convert to Array: Use the spread syntax (...) or Array.from() to create a new array from the Set.
  2. Sort the Array: Use the Array.prototype.sort() method on the new array.
  3. Convert Back to Set (Optional): If you need the final result to be a Set, pass the sorted array to the new Set() constructor.

Sorting a Set of Strings (Alphabetical Sort)​

When sorting an array of strings, the default behavior of sort() is alphabetical, which is exactly what we need.

Solution: this is the most concise and modern way to sort a Set of strings.

const mySet = new Set(['cherry', 'apple', 'banana']);

// 1. Convert to an array and sort it.
const sortedArray = [...mySet].sort();

console.log(sortedArray); // Output: ['apple', 'banana', 'cherry']

// 2. (Optional) Convert the sorted array back into a Set.
const sortedSet = new Set(sortedArray);

console.log(sortedSet);   // Output: Set(3) { 'apple', 'banana', 'cherry' }

Output:

['apple', 'banana', 'cherry']
Set(3) {'apple', 'banana', 'cherry'}
note

You can also perform this in a single, chained line:

const sortedSet = new Set([...mySet].sort());

Sorting a Set of Numbers (Numerical Sort)​

This is a critical case that often trips up beginners. The default sort() method converts elements to strings before comparing them. This leads to incorrect results for numbers.

Problem: Incorrect Sort

const numberSet = new Set([10, 2, 100]);

// WRONG: This sorts alphabetically ("10", "100", "2")
const incorrectlySorted = [...numberSet].sort();

console.log(incorrectlySorted);

Output: (This is NOT correct!)

[10, 100, 2]

The solution to sort numbers correctly is that you must provide a compare function to the sort() method. For ascending order, the function is (a, b) => a - b.

const numberSet = new Set([10, 2, 100]);

// CORRECT: Use a compare function for a numerical sort.
const sortedArray = [...numberSet].sort((a, b) => a - b);

console.log(sortedArray); // Output: [2, 10, 100]

// Optional: Convert back to a Set
const sortedSet = new Set(sortedArray);
console.log(sortedSet);   // Output: Set(3) { 2, 10, 100 }

Output:

[2, 10, 100]
Set(3) {2, 10, 100}

Conclusion​

While Set objects do not have a native .sort() method, they can be easily sorted by leveraging the power of Array.prototype.sort().

  • The standard process is: Set -> Array -> sort() -> Set.
  • The most modern and concise way to convert a Set to an Array is with the spread syntax ([...mySet]).
  • For strings, a simple .sort() is sufficient.
  • For numbers, you must provide a compare function to ensure a correct numerical sort: .sort((a, b) => a - b).

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