String.prototype.localeCompare()

localeCompare(compareString[, locales[, options]])

The localeCompare() method compares two strings in the current locale (or a specified locale) and returns a number indicating whether the reference string comes before, after, or is equivalent to the compared string in sort order. This is essential for building multilingual applications that need locale-aware sorting and searching.

Syntax

localeCompare(compareString)
localeCompare(compareString, locales)
localeCompare(compareString, locales, options)

Parameters

Parameter	Type	Default	Description
compareString	string	—	The string to compare against
locales	string or array	undefined	BCP 47 language tag(s) (e.g., ‘en-US’, ‘de-DE’)
options	object	undefined	Configuration for comparison behavior

Options Object

Property	Type	Description
sensitivity	string	’base’, ‘accent’, ‘case’, ‘variant’
ignorePunctuation	boolean	Whether to ignore punctuation
numeric	boolean	Whether to use numeric ordering
caseFirst	string	’upper’ or ‘lower’

Return Value

Returns a negative number if the reference string sorts before compareString, a positive number if it sorts after, or 0 if they are equivalent.

Examples

Basic Comparison

const str = 'apple';

str.localeCompare('banana');   // -1 (apple comes before banana)
str.localeCompare('apple');    // 0 (equal)
str.localeCompare('zebra');    // 1 (apple comes after zebra)

Locale-Aware Sorting

const fruits = ['banana', 'Apple', 'cherry'];

// Default comparison
fruits.sort((a, b) => a.localeCompare(b));
// Result: ['Apple', 'banana', 'cherry']

// German phonebook ordering
fruits.sort((a, b) => a.localeCompare(b, 'de-DE'));

Numeric Sorting

const versions = ['v10', 'v2', 'v1', 'v20'];

// Numeric sorting (v1, v2, v10, v20 instead of v1, v10, v2, v20)
versions.sort((a, b) => a.localeCompare(b, undefined, { numeric: true }));
// Result: ['v1', 'v2', 'v10', 'v20']

Browser Support

Supported in all modern browsers. Internet Explorer requires version 6+. For older browsers, consider using a polyfill.

See Also

• string::toLowerCase — Convert to lowercase
• string::toUpperCase — Convert to uppercase