js之数字每三位加逗号

function toThousands(num) {

  num = (num || 0).toString();

  let number = 0,

      floatNum = '',

      intNum = '';

  // 判断是否有小数位，有则截取小数点后的数字

  if (num.indexOf('.') > 0) {

    number = num.indexOf('.'); // 获取小数点出现的位置

    floatNum = num.substr(number); // 截取arr.substr(form, length)

    intNum = num.substring(0,number); // 截取arr.substring(start, end)

  } else {

    intNum = num;

  }

  let result = [],

      counter = 0;

  intNum = intNum.split('');

  // 利用3的倍数，向数组插入','

  for (let i = intNum.length - 1; i >= 0; i--) {

    counter++;

    result.unshift(intNum[i]);

    if (!(counter % 3) && i != 0) { result.unshift(','); }

  }

  return result.join('') + floatNum || '';

}

const A1 = 1234567890122;

const A2 = 1234567890122.122;

console.log(toThousands(A1)); //1,234,567,890,122

console.log(toThousands(A2)); // 1,234,567,890,122.122