Compare alphanumeric strings the same way a human would, using a natural order algorithm
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String Natural Compare

Compare alphanumeric strings the same way a human would, using a natural order algorithm

NPM Version Build Status Coverage Status devDependencies Status

Standard sorting:   Natural order sorting:
    img1.png            img1.png
    img10.png           img2.png
    img12.png           img10.png
    img2.png            img12.png

This module provides two functions:

  • naturalCompare
  • naturalCompare.caseInsensitive (alias: naturalCompare.i)

These functions return a number indicating whether one string should come before, after, or is the same as another string. They can be easily used with the native .sort() array method.

Fast and Robust

This module uses a performant and robust algorithm to compare alphanumeric strings. It can compare strings containing any size of number and is heavily tested with a custom benchmark suite to make sure that it is as fast as possible, even when a custom alphabet has been configured.


# npm
npm install string-natural-compare --save

# yarn
yarn add string-natural-compare


var naturalCompare = require('string-natural-compare');

// Simple case-sensitive sorting
var a = ['z1.doc', 'z10.doc', 'z17.doc', 'z2.doc', 'z23.doc', 'z3.doc'];
// -> ['z1.doc', 'z2.doc', 'z3.doc', 'z10.doc', 'z17.doc', 'z23.doc']

// Simple case-insensitive sorting
var a = ['B', 'C', 'a', 'd'];
a.sort(naturalCompare.caseInsensitive); // alias: a.sort(naturalCompare.i);
// -> ['a', 'B', 'C', 'd']

// Note:
['a', 'A'].sort(naturalCompare.caseInsensitive); // -> ['a', 'A']
['A', 'a'].sort(naturalCompare.caseInsensitive); // -> ['A', 'a']

// Compare strings containing large numbers
// -> 1
// Other inputs with the same ordering as this may yield a different number > 0

// In most cases we want to sort an array of objects
var a = [
  {street: '350 5th Ave', room: 'A-1021'},
  {street: '350 5th Ave', room: 'A-21046-b'}

// Sort by street (case-insensitive), then by room (case-sensitive)
a.sort(function(a, b) {
  return (
    naturalCompare.caseInsensitive(a.street, b.street) ||

// When text transformation is needed or when doing a case-insensitive sort on a
// large array, it is best for performance to pre-compute the transformed text
// and store it in that object. This way, the text transformation will not be
// needed for every comparison when sorting.
var a = [
  {make: 'Audi', model: 'R8'},
  {make: 'Porsche', model: '911 Turbo S'}

// Sort by make, then by model (both case-insensitive)
a.forEach(function(car) {
  car.sortKey = (car.make + ' ' + car.model).toLowerCase();
a.sort(function(a, b) {
  return naturalCompare(a.sortKey, b.sortKey);

Custom Alphabet

It is possible to configure a custom alphabet to achieve a desired character ordering.

// Estonian alphabet
naturalCompare.alphabet = 'ABDEFGHIJKLMNOPRSŠZŽTUVÕÄÖÜXYabdefghijklmnoprsšzžtuvõäöüxy';
['t', 'z', 'x', 'õ'].sort(naturalCompare);
// -> ['z', 't', 'õ', 'x']

// Russian alphabet
naturalCompare.alphabet = 'АБВГДЕЁЖЗИЙКЛМНОПРСТУФХЦЧШЩЪЫЬЭЮЯабвгдеёжзийклмнопрстуфхцчшщъыьэюя';
['Ё', 'А', 'б', 'Б'].sort(naturalCompare);
// -> ['А', 'Б', 'Ё', 'б']

Note: Putting numbers in the custom alphabet can cause undefined behaviour.