code: function round(number, prec) {
      number = number == undefined ? 0 : number
      number = (number + '').replace(/[^0-9+-Ee.]/g, '')
      var n = !isFinite(+number) ? 0 : +number,
          prec = !isFinite(+prec) ? 0 : Math.abs(prec)
  
      var k = Math.pow(10, prec)
      return Math.round(number * k) / k
  }
docs: 四舍5入