File Input accept Attribute
The HTML5 revolution provided us several simple but important attributes like download, autofocus, required, novalidate, and placeholder. There's another one you may want to know about: accept. The accept attribute is useful for input[type=file] elements. Let's have a look at it!
The HTML
I'll use Twitter's upload button to illustrate a good usage of the accept attribute:
<input type="file" name="media_empty" accept="image/gif,image/jpeg,image/jpg,image/png,">
The accept attribute gets a comma-separated list of mime types for files desired file types. In this case, Twitter is allowing the user to upload common image formats.
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The biggest problem about using this code is that the user can change it easily with firebug or others debugs.
It’s not for validation, it’s for assisting the user to select the right file type (since the file selection will only show files of that type).
You should never use this for validation since some browsers do not support it.
Validation should be done on your backend. This kind of selection only helps users what we really need from them.
Be careful with this.
The main issue is that some mobile browsers started to prevent the user from selecting any (!) file at all if the accept property was declared (which is just plain terrible user agent behaviour).
Thus if you want to support these browsers, you have to detect them and remove the accept property.
For details see http://caniuse.com/#feat=input-file-accept