Html input file控件使用accept过滤文件 ，老的浏览器不支持，不过对应新的浏览器还是方便很多
<input type="file" accept=".txt" >
弹出的文件选择框值显示txt文件
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input type=file accept中可以限制的文件类型
accept这个属性，只在FF，ie10和chrome中有效。那么accept能限制哪些文件呢？见下表。 MIME 描述
| *.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 |