向上取数

取两个数组中的最大值，然后将向上取整，如14000，变成20000.

getYMax(ay1, ay2){
        let ay = ay1.concat(ay2)
        let max =  Math.floor(Math.max(...ay))
        // let max = Math.floor(ay[ay.length-1])
        let value  = 1
        let length = max.toString().length -1
        for(let i = 0; i < length; i++){
          value = value * 10
        }
        let showMax =  Math.ceil(max/value) * value
        return  showMax
      },