获取数组的随机数

 getRondom (arr, len) {
      var out = []

      while (len) {
        var index = Math.floor(Math.random() * arr.length)

        if (out.includes(index)) {

        } else {
          arr.splice(index, 1)
          out = out.concat(index)
          len--
        }
      }

      return out
    }