js 随机生成之间的数（包括小数和负数）

getRandomNum: function(minNum, maxNum, decimalNum) {

    var max = 0, min = 0

    minNum <= maxNum ? (min = minNum, max = maxNum) : (min = maxNum, max = minNum)

    switch (arguments.length) {

      case 1:

        return Math.floor(Math.random() * (max + 1))

      case 2:

        return Math.floor(Math.random() * (max - min + 1) + min)

      case 3:

        return (Math.random() * (max - min) + min).toFixed(decimalNum)

      default:

        return Math.random()

    }

  },