回答

需要修改源码upload.js源码,搜索y=function(){

将后面的代码更换成

return "choose" === t ? l.choose && l.choose(g) : ((l.before && l.before(g)) === false ? '' : a.ie ? a.ie > 9 ? u() : c() : void u())

const uploadInst = upload.render({
            elem: '#exportBtn',
            url: config.base_server,
            accept: 'file',
            exts: 'xls|xlsx|XLS|XLS',
            auto: false,
            choose: function (obj) {
                uploadInst.config.elem.next()[0].value = '';
                obj.preview(function (index, file) {
                    obj.upload(index, file)
                });
            },
            before: function (obj) {
                 return false;//取消上传
                layer.load(2);
            },
            done: function (res) {
                layer.closeAll('loading');
                layer.msg("上传成功", {icon: 1});
            },
            error: function () {
                layer.closeAll('loading');
                layer.msg("上传失败", {icon: 2});
            }
        });