金钱格式化(整数)

//正则

let cash = '1234567890'

cash.replace(/\B(?=(\d{3})+(?!\d))/g, ',');//"1,234,567,890"

//非正则的优雅实现

function formatCash(str) {

 return str.split('').reverse().reduce((prev, next, index) => {

 return ((index % 3) ? next : (next + ',')) + prev

 })

}

formatCash(cash);//"1,234,567,890"