code: function addNum (num1, num2) {
    let sq1, sq2
    try {
      sq1 = _toString(num1).split('.')[1].length
    } catch (e) {
      sq1 = 0
    }
    try {
      sq2 = _toString(num2).split('.')[1].length
    } catch (e) {
      sq2 = 0
    }
    const m = Math.pow(10, Math.max(sq1, sq2))
    return (Math.round(num1 * m) + Math.round(num2 * m)) / m
  }
docs: 实现两数相加并保留小数点后最短尾数