Binding buttons to textbox

I created this jFi开发者_如何学运维ddle here: http://jsfiddle.net/NkxHD/3/ in which I want to bind buttons to textbox. So if I click '7' I want 7 to be displayed in the textbox. Something like this:

function(e){} --

How should I do this?

Here's an update

and here is more complete one:

Click Me

here is the update I add a class "number" to each number button so that the event will not be fired with other buttons.