今天使用bootstrap-fileinput做文件上传时候，报出下面的异常

fileinput.min.js:11 Uncaught TypeError: Cannot read property 'length' of undefined
    at i._uploadExtra (VM5937 fileinput.min.js:11)
    at i._ajaxSubmit (VM5937 fileinput.min.js:11)
    at i._uploadSingle (VM5937 fileinput.min.js:11)
    at i.upload (VM5937 fileinput.min.js:12)
    at i._uploadClick (VM5937 fileinput.min.js:11)
    at HTMLAnchorElement.i (VM5896 jquery.min.js:29)
    at HTMLAnchorElement.dispatch (VM5896 jquery.min.js:29)
    at HTMLAnchorElement.v.handle (VM5896 jquery.min.js:29)

之前有用该组件做过一个同样的功能，那个上传是没有问题的，于是就对比了一下代码，发现是在下面代码中扩展参数uploadExtraData方法内注释了return那行导致的问题。

function initUpload(ctrlName, uploadUrl) {
        var control = $('#' + ctrlName);
        control.fileinput({
            language: 'zh', //设置语言
            uploadUrl: uploadUrl, //上传的地址
            uploadAsync: true, //默认异步上传
            showCaption: true,//是否显示标题
            showUpload: true, //是否显示上传按钮
            browseClass: "btn btn-primary", //按钮样式
            allowedFileExtensions: ["xls", "xlsx"], //接收的文件后缀
            maxFileCount: 10,//最大上传文件数限制
            previewFileIcon: '<i class="glyphicon glyphicon-file"></i>',
            showPreview: true, //是否显示预览
            previewFileIconSettings: {
                'docx': '<i ass="fa fa-file-word-o text-primary"></i>',
                'xlsx': '<i class="fa fa-file-excel-o text-success"></i>',
                'xls': '<i class="fa fa-file-excel-o text-success"></i>',
                'pptx': '<i class="fa fa-file-powerpoint-o text-danger"></i>',
                'jpg': '<i class="fa fa-file-photo-o text-warning"></i>',
                'pdf': '<i class="fa fa-file-archive-o text-muted"></i>',
                'zip': '<i class="fa fa-file-archive-o text-muted"></i>',
            },
            uploadExtraData: function () {//扩展参数
                /* return {"apartmentId": ${apartmentId}}; */
            }
        });
    }

解决办法

既然已经知道了问题所在，那就解决起来就简单了，下面是两种解决办法：
方法1、返回一个空的参数数组

function initUpload(ctrlName, uploadUrl) {
        var control = $('#' + ctrlName);
        control.fileinput({
            language: 'zh', //设置语言
            uploadUrl: uploadUrl, //上传的地址
            uploadAsync: true, //默认异步上传
            showCaption: true,//是否显示标题
            showUpload: true, //是否显示上传按钮
            browseClass: "btn btn-primary", //按钮样式
            allowedFileExtensions: ["xls", "xlsx"], //接收的文件后缀
            maxFileCount: 10,//最大上传文件数限制
            previewFileIcon: '<i class="glyphicon glyphicon-file"></i>',
            showPreview: true, //是否显示预览
            previewFileIconSettings: {
                'docx': '<i ass="fa fa-file-word-o text-primary"></i>',
                'xlsx': '<i class="fa fa-file-excel-o text-success"></i>',
                'xls': '<i class="fa fa-file-excel-o text-success"></i>',
                'pptx': '<i class="fa fa-file-powerpoint-o text-danger"></i>',
                'jpg': '<i class="fa fa-file-photo-o text-warning"></i>',
                'pdf': '<i class="fa fa-file-archive-o text-muted"></i>',
                'zip': '<i class="fa fa-file-archive-o text-muted"></i>',
            },
            uploadExtraData: function () {//扩展参数
                 return { };
            }
        });
    }

方法2、如果没有扩展参数，删除uploadExtraData属性就可以了

function initUpload(ctrlName, uploadUrl) {
        var control = $('#' + ctrlName);
        control.fileinput({
            language: 'zh', //设置语言
            uploadUrl: uploadUrl, //上传的地址
            uploadAsync: true, //默认异步上传
            showCaption: true,//是否显示标题
            showUpload: true, //是否显示上传按钮
            browseClass: "btn btn-primary", //按钮样式
            allowedFileExtensions: ["xls", "xlsx"], //接收的文件后缀
            maxFileCount: 10,//最大上传文件数限制
            previewFileIcon: '<i class="glyphicon glyphicon-file"></i>',
            showPreview: true, //是否显示预览
            previewFileIconSettings: {
                'docx': '<i ass="fa fa-file-word-o text-primary"></i>',
                'xlsx': '<i class="fa fa-file-excel-o text-success"></i>',
                'xls': '<i class="fa fa-file-excel-o text-success"></i>',
                'pptx': '<i class="fa fa-file-powerpoint-o text-danger"></i>',
                'jpg': '<i class="fa fa-file-photo-o text-warning"></i>',
                'pdf': '<i class="fa fa-file-archive-o text-muted"></i>',
                'zip': '<i class="fa fa-file-archive-o text-muted"></i>',
            }
        });
    }