index.js

const locale = require('locale')


supported = new locale.Locales(['en', 'en_US'], 'en');
console.log ((new locale.Locales('en')).best(supported).toString());     // 'en'
console.log ((new locale.Locales('en_GB')).best(supported).toString());  // 'en'
console.log ((new locale.Locales('en_US')).best(supported).toString());  // 'en_US'
console.log ((new locale.Locales('jp')).best(supported).toString());  // en


supported = new locale.Locales(['zh-Hans', 'en-SG'], 'zh-Hans');
console.log ((new locale.Locales('en')).best(supported).toString());     // 'en-SG'
console.log ((new locale.Locales('en_GB')).best(supported).toString());  // 'en-SG'
console.log ((new locale.Locales('en_US')).best(supported).toString());  // 'en-SG'
console.log ((new locale.Locales('jp')).best(supported).toString()); // zh-Hans

package.json

{
  "name": "localetest",
  "version": "1.0.0",
  "description": "",
  "main": "index.js",
  "scripts": {
    "test": "echo \"Error: no test specified\" && exit 1"
  },
  "author": "",
  "license": "ISC",
  "dependencies": {
    "locale": "^0.1.0"
  }
}