数字格式化10000 => 10k

/**
 * 数字格式化10000 => 10k
 * @param num 需要格式化的数字
 * @param digits 小数保留位数
 */
function numberFormatter(num, digits) {
  const si = [
    {value: 1E18, symbol: 'E'},
    {value: 1E15, symbol: 'P'},
    {value: 1E12, symbol: 'T'},
    {value: 1E9, symbol: 'G'},
    {value: 1E6, symbol: 'M'},
    {value: 1E3, symbol: 'k'}
  ];
  for (let i = 0; i < si.length; i++) {
    if (num >= si[i].value) {
      return (num / si[i].value).toFixed(digits).replace(/\.0+$|(\.[0-9]*[1-9])0+$/, '$1') + si[i].symbol
    }
  }
  return num.toString();
}

//用法：
numberFormatter(12345678, 3); // 12.346M