If input value is blank, assign a value of "empty" with Javascript
This can be done using HTML5's placeHolder or using JavaScript. Checkout this post.
If you're using pure JS you can simply do it like:
var input = document.getElementById('myInput');
if(input.value.length == 0)
input.value = "Empty";
Here's a demo: http://jsfiddle.net/nYtm8/
I'm guessing this is what you want...
When the form is submitted, check if the value is empty and if so, send a value = empty.
If so, you could do the following with jQuery.
$('form').submit(function(){
var input = $('#test').val();
if(input == ''){
$('#test').val('empty');
}
});
HTML
<form>
<input id="test" type="text" />
</form>
http://jsfiddle.net/jasongennaro/NS6Ca/
Click your cursor in the box and then hit enter to see the form submit the value.