Pass filename from file upload to text field

Here's one way to do it

document.getElementById('upload').onchange = uploadOnChange;

function uploadOnChange() {
  var filename = this.value;
  var lastIndex = filename.lastIndexOf("\\");
  if (lastIndex >= 0) {
    filename = filename.substring(lastIndex + 1);
  }
  document.getElementById('filename').value = filename;
}

<input id="upload" type="file" />
<input id="filename" type="text" />

you don't mention jQuery but given it's popularity here's the same solution using jQuery

jQuery:

$('#upload').change(function() {
    var filename = $(this).val();
    var lastIndex = filename.lastIndexOf("\\");
    if (lastIndex >= 0) {
        filename = filename.substring(lastIndex + 1);
    }
    $('#filename').val(filename);
});

Demo:

http://jsfiddle.net/pxfunc/WWNnV/4/