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.

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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?

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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.