網頁上新增一個input file HTML控制元件：
<input id="File1" type="file" />
預設是這樣的，所有檔案型別都會顯示出來，如果想限制它只顯示我們設定的檔案型別呢，比如“word“,”excel“,”pdf“檔案
解決辦法是可以給它新增一個accept屬性，比如：
<input id="File1" type="file" accept=".xls,.doc,.txt,.pdf" />
這樣選擇的時候預設會顯示為這樣：
檔案選擇框內只顯示出你自定義檔案型別的檔案，也還比較方便。
But,這只是最簡單的掩人耳目的做法，還是能選擇其它檔案型別：
所以，如果要做到真正意義上限制型別做法（其實這種算不上限制，只是把你要的檔案型別預設顯示出來而已，並不是說不能選擇其它的），還是要通過js或者後臺來控制。
附支援的檔案型別：
*.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 *.pdf 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