How to call this fucntion from text box

[JohnSmith]

I have a text box and I want the function to run only if the user has clicked or tab over to the TxtBox1 and the user presses F9 on their keyboard



document.onkeyup = handleKeyUp;

function handleKeyUp(e)
{
if(!e)
var e = window.event;

key = e.keyCode;
Frm.txtBox1.value = key;

if (key == 120)
{
alert("You pressed F9 key");
}

}