use browser locales

CHANGELOG.md

@@ -4,6 +4,9 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
+## [6.1.0] - 2023-03-11
+- Defaults to browser locales from `navigator.languages`
+
 ## [6.0.2] - 2023-03-11
 - Update readme
 

lib/millify.ts

@@ -1,5 +1,5 @@
 import { defaultOptions, MillifyOptions } from "./options";
-import { getFractionDigits, parseValue, roundTo } from "./utils";
+import { getFractionDigits, getLocales, parseValue, roundTo } from "./utils";
 
 // Most commonly used digit grouping base.
 const DIGIT_GROUPING_BASE = 1000;
@@ -98,7 +98,7 @@ function millify(value: number, options?: Partial<MillifyOptions>): string {
   const space = opts.space ? " " : "";
 
   // Format the number according to the desired locale.
-  const formatted = rounded.toLocaleString(opts.locales, {
+  const formatted = rounded.toLocaleString(opts.locales ?? getLocales(), {
     // toLocaleString needs the explicit fraction digits.
     minimumFractionDigits: getFractionDigits(rounded),
   });

lib/utils.ts

@@ -39,3 +39,13 @@ export function getFractionDigits(num: number): number {
   const decimalPart = num.toString().split(".")[1];
   return decimalPart?.length ?? 0;
 }
+
+/**
+ * Returns the default browser locales.
+ */
+export function getLocales(): string[] {
+  if (typeof navigator === "undefined") {
+    return [];
+  }
+  return Array.from(navigator.languages ?? []);
+}