以下是代码块，不知何原因总是报 indexOf  undefined 好长时间了，求解，谢谢啦

downloadlist: function (options) {

var _this = this

var FileSystemManager = wx.getFileSystemManager();//声明文件管理器

var paths = wx.env.USER_DATA_PATH;

try {

var downloadlist = FileSystemManager.readdirSync(paths)

if (downloadlist.length >= 1) {

if (downloadlist.length == 1 && downloadlist[0] == "miniprogramLog") {

_this.setData({

hidden: true,

load: false

})

} else {

var newFilenameArr = []

for (var i = 0; i < downloadlist.length; i++) {

var filename = downloadlist[i]

var extensionarr = filename.split(".");

var filenamearr = extensionarr[0].split("_");

switch (filenamearr[0]) {

case 'level1':

var level = "预备级上";

break;

case 'level2':

var level = "预备级下";

break;

case 'level3':

var level = "一级上";

break;

case 'level4':

var level = "一级下";

break;

case 'level5':

var level = "二级上";

break;

case 'level6':

var level = "二级下";

break;

case 'level7':

var level = "三级上";

break;

case 'level8':

var level = "三级下";

break;

}

var filename = filenamearr[0] + '_' + filenamearr[1] + '_' + filenamearr[2] + '.' + extensionarr[1]

var idsting = filenamearr[0] + '_' + filenamearr[1] + '_' + filenamearr[2]

if (filenamearr[0] && filenamearr[1] && filenamearr[2] && filenamearr[0] !== 'miniprogramLog' && filenamearr[1] !== 'miniprogramLog' && filenamearr[2] !== 'miniprogramLog') {

var newarray = {

level: level,

unit: filenamearr[1],

part: filenamearr[2],

filePath: wx.env.USER_DATA_PATH + '/' + filenamearr[0] + '_' + filenamearr[1] + '_' + filenamearr[2] + '.' + extensionarr[1],

idsting: idsting,

isTouchMove: false //默认隐藏删除

}

newFilenameArr[i] = newarray

}

}

_this.setData({

downloadlistarr: newFilenameArr,

load: false

})

}

} else {

_this.setData({

hidden: true,

load: false

})

}

} catch (e) {

console.log(e)

}

},