/**

 * Quantity of a number. e.g. 0.1, 1, 10, 100

 *

 * @param  {number} val

 * @return {number}

 */

function quantity(val) {

    return Math.pow(10, quantityExponent(val));

}

function quantityExponent(val) {

    return Math.floor(Math.log(val) / Math.LN10);

}

/**

 * find a “nice” number approximately equal to x. Round the number if round = true,

 * take ceiling if round = false. The primary observation is that the “nicest”

 * numbers in decimal are 1, 2, and 5, and all power-of-ten multiples of these numbers.

 *

 * See "Nice Numbers for Graph Labels" of Graphic Gems.

 *

 * @param  {number} val Non-negative value.

 * @param  {boolean} round

 * @return {number}

 */

function nice(val, round) {

  console.log('get real splitNum==1111===>', val, round);

    var exponent = quantityExponent(val);

    var exp10 = Math.pow(10, exponent);

    var f = val / exp10; // 1 <= f < 10

    var nf;

    if (round) {

        if (f < 1.5) {

            nf = 1;

        }

        else if (f < 2.5) {

            nf = 2;

        }

        else if (f < 4) {

            nf = 3;

        }

        else if (f < 7) {

            nf = 5;

        }

        else {

            nf = 10;

        }

    }

    else {

        if (f < 1) {

            nf = 1;

        }

        else if (f < 2) {

            nf = 2;

        }

        else if (f < 3) {

            nf = 3;

        }

        else if (f < 5) {

            nf = 5;

        }

        else {

            nf = 10;

        }

    }

    val = nf * exp10;

    // Fix 3 * 0.1 === 0.30000000000000004 issue (see IEEE 754).

    // 20 is the uppper bound of toFixed.

  const nice = exponent >= -20 ? +val.toFixed(exponent < 0 ? -exponent : 0) : val;

    return nice;

}

// val 传递的是: (你当前data数组中的最大值 / (splitNumber | 5))

// splitNumber 是你写的分割段数 如果没有设置 则使用5相除

// round 传false

// 例如 我这里传24

nice(24,false); // 返回20, 其中20 就是 步长值

// 如果是堆叠图表 需要进行数据相加后 获取相加后的数组的最大值 然后进行计算
nice(37, false); //