javascript - Detect when a browser page window loses focus with Alt-Tab using pure JS or jQuery

Question

Is it possible to detect current page is in alt-tab? This code works only if a new tab in browser is opened:

(function() {
  var hidden = "hidden";

  // Standards:
  if (hidden in document)
    document.addEventListener("visibilitychange", onchange);
  else if ((hidden = "mozHidden") in document)
    document.addEventListener("mozvisibilitychange", onchange);
  else if ((hidden = "webkitHidden") in document)
    document.addEventListener("webkitvisibilitychange", onchange);
  else if ((hidden = "msHidden") in document)
    document.addEventListener("msvisibilitychange", onchange);
  // IE 9 and lower:
  else if ("onfocusin" in document)
    document.onfocusin = document.onfocusout = onchange;
  // All others:
  else
    window.onpageshow = window.onpagehide
    = window.onfocus = window.onblur = onchange;

  function onchange (evt) {
    var v = "visible", h = "hidden",
        evtMap = {
          focus:v, focusin:v, pageshow:v, blur:h, focusout:h, pagehide:h
        };

    evt = evt || window.event;
    if (evt.type in evtMap)
      document.body.className = evtMap[evt.type];
    else
      document.body.className = this[hidden] ? "hidden" : "visible";
  //console.log(this[hidden] ? "hidden" : "visible");
  }

  // set the initial state (but only if browser supports the Page Visibility API)
  if( document[hidden] !== undefined )
    onchange({type: document[hidden] ? "blur" : "focus"});
})();

But this code does detect neither new window of the browser nor alt-tab into any other programm. Is it possible to detect it? Or in jQuery?

EDIT New page means Ctrl(cmd)+N (new window) hotkey. The code above can not detect this. Alt(cmd)+tab to another program - impossible to detect too. The code above can only detect Ctrl(cmd)+T (new tab)

EDIT I want to detect when a user return to my site from another application. That is, if a user closes any tab (e.g., by Ctrl+W) and returns to my site I can detect this action using the script above. But if a user returns to my site from another application (e.g., by Alt+Tab) the script doesn't work because window.onfocus will not be fired! That is,

 window.onpageshow =
 window.onpagehide = window.onfocus = window.onblur 

doesn't work for Alt+Tab action. Is it more clear?

Answer 1

You can simply use the onfocus event on window, like in:

window.onfocus = function() {
  console.log('Got focus');
}

If needed, you can also use onblur for a more acute handling.