restrict file upload selection to specific types

Anyway to restrict the selection of file types via the <input type="file" /> element?

For instance, 开发者_如何转开发if I wanted only images types to be uploaded, I would restrict the possible selections to (image/jpg,image/gif,image/png), and the selection dialog would grey out files of other mime types.

p.s. I know that I can do this after the fact with the File API by scanning the .type attributes. I'm really trying to restrict this before hand.. I also know I can do this via flash, but I do NOT want to have use flash for this.

There is an html attribute for this specific purpose called accept but it has little support across browsers. Because of this server side validation is recommended instead.

<input type="file" name="pic" id="pic" accept="image/gif, image/jpeg" />

If you don't have access to the backend have a look at a flash based solution like SWFUpload.

See more on this here: File input 'accept' attribute - is it useful?

It's better to let user select any file, and then check its type - this is better supported by the browsers:

var
    file = (el[0].files ? el[0].files[0] : el[0].value || undefined),
    supportedFormats = ['image/jpg','image/gif','image/png'];

if (file && file.type) {
    if (0 > supportedFormats.indexOf(file.type)) {
        alert('unsupported format');
    }
    else {
        upload();
    }
}

You can also check for file size using file.size property.