数字添加千位符

// 千位符
export function toThousands(num) {
  if (!num) {
    return '0.00'
  }
  if (!/^(\+|-)?(\d+)(\.\d+)?$/.test(num)) {
    return num
  }
  var a = RegExp.$1; var b = RegExp.$2; var c = RegExp.$3
  var re = new RegExp().compile('(\\d)(\\d{3})(,|$)')
  while (re.test(b)) {
    b = b.replace(re, '$1,$2$3')
  }
  return a + '' + b + '' + c
}