Clearing <input type='file' /> using jQuery

Quick answer: replace it.

In the code below I use the replaceWith jQuery method to replace the control with a clone of itself. In the event you have any handlers bound to events on this control, we'll want to preserve those as well. To do this we pass in true as the first parameter of the clone method.

<input type="file" id="control"/>
<button id="clear">Clear</button>

var control = $("#control");

$("#clear").on("click", function () {
    control.replaceWith( control = control.clone( true ) );
});

Fiddle: http://jsfiddle.net/jonathansampson/dAQVM/

If cloning, while preserving event handlers, presents any issues you could consider using event delegation to handle clicks on this control from a parent element:

$("form").on("focus", "#control", doStuff);

This prevents the need for any handlers to be cloned along with the element when the control is being refreshed.

In IE8 they made the File Upload field read-only for security. See the IE team blog post:

Historically, the HTML File Upload Control () has been the source of a significant number of information disclosure vulnerabilities. To resolve these issues, two changes were made to the behavior of the control.

To block attacks that rely on “stealing” keystrokes to surreptitiously trick the user into typing a local file path into the control, the File Path edit box is now read-only. The user must explicitly select a file for upload using the File Browse dialog.

Additionally, the “Include local directory path when uploading files” URLAction has been set to "Disable" for the Internet Zone. This change prevents leakage of potentially sensitive local file-system information to the Internet. For instance, rather than submitting the full path C:\users\ericlaw\documents\secret\image.png, Internet Explorer 8 will now submit only the filename image.png.

The value of file inputs is read only (for security reasons). You can't blank it programatically (other than by calling the reset() method of the form, which has a broader scope than just that field).

function clear() {
    var input = document.createElement("input");
    input.setAttribute('type', 'file');
    input.setAttribute('value', '');
    input.setAttribute('id', 'email_attach');

    $('#email_attach').replaceWith( input.cloneNode() );
}

it does not work for me:

$('#Attachment').replaceWith($(this).clone());
or 
$('#Attachment').replaceWith($('#Attachment').clone());

so in asp mvc I use razor features for replacing file input. at first create a variable for input string with Id and Name and then use it for showing in page and replacing on reset button click:

@{
    var attachmentInput = Html.TextBoxFor(c => c.Attachment, new { type = "file" });
}

@attachmentInput

<button type="button" onclick="$('#@(Html.IdFor(p => p.Attachment))').replaceWith('@(attachmentInput)');">--</button>

An easy way is changing the input type and change it back again.

Something like this:

var input = $('#attachments');
input.prop('type', 'text');
input.prop('type', 'file')