Jquery - Start a function after open button (from input="file") is pressed

how can I start a function after the open* button is pressed?

html

<form id=开发者_开发百科"xxx">
  <input id="yyy" type="file" />
</form>

js

$(function(){

    $('body').append('jq works <br />');

    $("#xxx").submit(function ()
    {
        
       $('body').append('start function<br />');
        
    });
    
});

jsfiddle http://jsfiddle.net/vGBaK/

edit:

I mean this button ->

---

You can use the change event, it wont fire if the same file is selected but if you also clear on the click event it should work.

see this JSFiddle

$(function(){

    $('body').append('jq works <br />');

    $("#xxx").submit(function ()
    {

       $('body').append('go >> <br />');

    });

    $("#yyy").change(function(){
        alert("changed");
    }).click(function(){
        $(this).val("")
    });

});

---

Here I assume open* button means browse button of your file input box,

 $("#yyy").click(function(){
        //alert("button clicked")
        // write your code
 })