自定义后缀名的限制:

比如设置了个自定义文件 xxx.abc 和 xxx.def

想要限制只上传这种类型的文件 则直接写 

<input type="file" accept=".abc,.def" />

这里不需要使用*或者官方文档里写的"|" 符号, 只需要用逗号分隔开就行了

Valid Accept Types:

For CSV files (.csv), use: 

<input type="file" accept=".csv" />

For Excel Files 2003-2007 (.xls), use: 

<input type="file" accept="application/vnd.ms-excel" />

For Excel Files 2010 (.xlsx), use: 

<input type="file" accept="application/vnd.openxmlformats-officedocument.spreadsheetml.sheet" />

For Text Files (.txt) use: 

<input type="file" accept="text/plain" />

For Image Files (.png/.jpg/etc), use: 

<input type="file" accept="image/*" />

For HTML Files (.htm,.html), use:

<input type="file" accept="text/html" />

For Video Files (.avi, .mpg, .mpeg, .mp4), use:

<input type="file" accept="video/*" />

For Audio Files (.mp3, .wav, etc), use:

<input type="file" accept="audio/*" />

For PDF Files, use:

<input type="file" accept=".pdf" /> 

DEMO:
http://jsfiddle.net/dirtyd77/LzLcZ/144/

NOTE:

If you are trying to display Excel CSV files (.csv), do NOT use:

• text/csv
• application/csv
• text/comma-separated-values (works in Opera only).

If you are trying to display a particular file type (for example, a WAV or PDF), then this will almost always work...

 <input type="file" accept=".FILETYPE" />