Detect focus initiated by tab key?

I want to detect the focus event of an element, but only if it was initiated by the user pressing the tab key. For example:

<input type="text" id="foo" />
<input type="text" id="detect" />

If the user is focused on #foo and presses Tab, I want the event to fire once #detect becomes focused (or a conditional inside the focus event to be true). Conversely, if the user simply clicks on the #detect field to focus it, I do not want the event to fire (or I want the conditional inside the focus event call to be false).

I don't want to use the keydown event of #foo and check if the tab key was pressed, as I want the approach to be independent of any other element.

I looked through the console output of the following code, but couldn't notice any real differences between the two methods of focusing:

$('#detect').on('focus', function(e){
   console.log(e); 
});

(fiddle)

Is this possible to accomplish in a relatively simple way?

I know you have accepted an answer but you could test the button pressed using the following:

$('#detect').on('focus', function(e){
    $(window).keyup(function (e) {
        var code = (e.keyCode ? e.keyCode : e.which);
        if (code == 9) {
           alert('I was tabbed!');
        }
    });
});

http://jsfiddle.net/LPGLm/1/

Edit: change the listener around:

$(window).keyup(function (e) {
    var code = (e.keyCode ? e.keyCode : e.which);
    if (code == 9 && $('#detect:focus').length) {
        alert('I was tabbed!');
    }
});

http://jsfiddle.net/LPGLm/7/

A more responsive solution would be to use two listeners:

var mousedown = false;
$('#detect').on('mousedown', function () {
    mousedown = true;
});

$('#detect').on('focusin', function () {
    if(!mousedown) {
        // logic
    }
    mousedown = false;
});

Fiddle showing the difference in speed:

http://jsfiddle.net/u2y45/1/

As you've noticed, the event object itself does not distinguish the means of access. What you can do is to bind a mousedown listener, which will fire before focus, and set some timestamp flag that you compare to some threshold value in your focus handler.

You can check focus event on specific input by this code

$(window).on('keyup', function(event){
    if(event.keyCode == '9'){
        
      getFocused(event);
    }

})
var focused = 0;
function getFocused(e){
var ida =  $(':focus').eq(0).prop('id');
    if(ida=='detect' && focused==0){
        focused = 1;
        console.log(e);
    }
}

(fiddle)

I use the following:

(function() {
  const tabHistory = [];

  window.addEventListener('keyup', function (e) {
    const code = e.keyCode || e.which;
    const index = tabHistory.length === 0 ? 1 : tabHistory.length + 1;

    if (code == 9) {
      tabHistory.push({
        element: e.target,
        index
      });

      console.log(index, e.target, tabHistory);
    }
  });
})();

I recommend keeping a track of the focused elements, this way you make sure the user will be able to tab as you expected.

Hope it helps!