Country & Region Codes

Practical Snippet

Key points: (1) flag emoji can only be built from alpha-2; numeric codes must first be converted via 127397 + n; (2) Windows may render a flag as two letters due to a missing platform font rather than an encoding error, so production should use SVG assets instead of relying on an emoji font; (3) use codes rather than country names as the primary key for pickers and storage, since official names change (Türkiye, Czechia) and a name-keyed list breaks on every ISO revision.

// 数字代码 → alpha-2 → 国旗 emoji
function numericToAlpha2(numeric: number): string {
  // UN M49 / ISO 3166-1 numeric 转 alpha-2：127397 是 'A' 的 regional indicator 码位
  return String.fromCodePoint(127397 + numeric)
}

function flagOf(alpha2: string): string {
  if (alpha2.length !== 2) throw new Error('flag needs alpha-2')
  const base = 0x1f1e6 // 'A' 的 regional indicator
  return String.fromCodePoint(
    base + (alpha2.toUpperCase().charCodeAt(0) - 65),
    base + (alpha2.toUpperCase().charCodeAt(1) - 65),
  )
}

console.log(numericToAlpha2(156))            // CN
console.log(flagOf('cn'))                  // 🇨🇳
console.log(flagOf('de'), flagOf('jp'))     // 🇩🇪 🇯🇵

// ⚠ Windows 上可能渲染成 "CN" 两个字母 —— 平台字体缺失，不是编码错误
// 生产环境应改用 <img src=".../cn.svg">，避免依赖 emoji 字体

// 下拉框的稳定主键：用 alpha-2，不要用国家名（会随 ISO 改版变化）
const options = [
  { code: 'CN', name: 'China' },
  { code: 'DE', name: 'Germany' },
]