（IE9及以下不支持下面这些功能，其它浏览器最新版本均已支持。）
1、允许上传文件数量
1. 允许选择多个文件：<input type="file" multiple>
2. 只允许上传一个文件：<input type="file" single>
2、上传指定的文件格式
如指定默认格式为gif、png：
<input type="file" accept="image/gif,image/png" />
如果不限制上传图片的格式，只限制图片可写成：accept="image/*"
这里的上传格式仅指打开上传弹窗选择文件时默认的文件格式，也可选择文件时手动修改成所有文件(*)，如下图：
限制上传.xls、.xlsx文件：
//限制.xls文件
accept="application/vnd.ms-excel"
//限制.xlsx文件
accept="application/vnd.openxmlformats-officedocument.spreadsheetml.sheet"
同时限制上传.xls、.xlsx文件
<input class="note-image-input form-control" type="file" name="files" accept="application/vnd.openxmlformats-officedocument.spreadsheetml.sheet,application/vnd.ms-excel " multiple="multiple">
这只是指定了选择文件的默认类型，真实限制类型还要用到JS代码
if (['xls','xlsx'].indexOf(FileExt.toLowerCase()) === -1){
this.$message.warning('只能上传.XLS.XLSX格式的文件!');
return false;
}
3.其他的accept的接受格式
| *.3gpp | audio/3gpp, video/3gpp | 3GPP Audio/Video |
| *.ac3 | audio/ac3 | AC3 Audio |
| *.asf | allpication/vnd.ms-asf | Advanced Streaming Format |
| *.au | audio/basic | AU Audio |
| *.css | text/css | Cascading Style Sheets |
| *.csv | text/csv | Comma Separated Values |
| *.doc | application/msword | MS Word Document |
| *.dot | application/msword | MS Word Template |
| *.dtd | application/xml-dtd | Document Type Definition |
| *.dwg | image/vnd.dwg | AutoCAD Drawing Database |
| *.dxf | image/vnd.dxf | AutoCAD Drawing Interchange Format |
| *.gif | image/gif | Graphic Interchange Format |
| *.htm | text/html | HyperText Markup Language |
| *.html | text/html | HyperText Markup Language |
| *.jp2 | image/jp2 | JPEG-2000 |
| *.jpe | image/jpeg | JPEG |
| *.jpeg | image/jpeg | JPEG |
| *.jpg | image/jpeg | JPEG |
| *.js | text/javascript, application/javascript | JavaScript |
| *.json | application/json | JavaScript Object Notation |
| *.mp2 | audio/mpeg, video/mpeg | MPEG Audio/Video Stream, Layer II |
| *.mp3 | audio/mpeg | MPEG Audio Stream, Layer III |
| *.mp4 | audio/mp4, video/mp4 | MPEG-4 Audio/Video |
| *.mpeg | video/mpeg | MPEG Video Stream, Layer II |
| *.mpg | video/mpeg | MPEG Video Stream, Layer II |
| *.mpp | application/vnd.ms-project | MS Project Project |
| *.ogg | application/ogg, audio/ogg | Ogg Vorbis |
| application/pdf | Portable Document Format | |
| *.png | image/png | Portable Network Graphics |
| *.pot | application/vnd.ms-powerpoint | MS PowerPoint Template |
| *.pps | application/vnd.ms-powerpoint | MS PowerPoint Slideshow |
| *.ppt | application/vnd.ms-powerpoint | MS PowerPoint Presentation |
| *.rtf | application/rtf, text/rtf | Rich Text Format |
| *.svf | image/vnd.svf | Simple Vector Format |
| *.tif | image/tiff | Tagged Image Format File |
| *.tiff | image/tiff | Tagged Image Format File |
| *.txt | text/plain | Plain Text |
| *.wdb | application/vnd.ms-works | MS Works Database |
| *.wps | application/vnd.ms-works | Works Text Document |
| *.xhtml | application/xhtml+xml | Extensible HyperText Markup Language |
| *.xlc | application/vnd.ms-excel | MS Excel Chart |
| *.xlm | application/vnd.ms-excel | MS Excel Macro |
| *.xls | application/vnd.ms-excel | MS Excel Spreadsheet |
| *.xlt | application/vnd.ms-excel | MS Excel Template |
| *.xlw | application/vnd.ms-excel | MS Excel Workspace |
| *.xml | text/xml, application/xml | Extensible Markup Language |
| *.zip | aplication/zip | Compressed Archive |
