Detect If Browser Tab Has Focus

Yes, window.onfocus and window.onblur should work for your scenario:

http://www.thefutureoftheweb.com/blog/detect-browser-window-focus

Important Edit: This answer is outdated. Since writing it, the Visibility API (mdn, example, spec) has been introduced. It is the better way to solve this problem.

var focused = true;window.onfocus = function() {    focused = true;};window.onblur = function() {    focused = false;};

AFAIK, focus and blur are all supported on...everything. (see http://www.quirksmode.org/dom/events/index.html )

While searching about this problem, I found a recommendation that Page Visibility API should be used. Most modern browsers support this API according to Can I Use: http://caniuse.com/#feat=pagevisibility.

Here's a working example (derived from this snippet):

$(document).ready(function() {  var hidden, visibilityState, visibilityChange;  if (typeof document.hidden !== "undefined") {    hidden = "hidden", visibilityChange = "visibilitychange", visibilityState = "visibilityState";  } else if (typeof document.msHidden !== "undefined") {    hidden = "msHidden", visibilityChange = "msvisibilitychange", visibilityState = "msVisibilityState";  }  var document_hidden = document[hidden];  document.addEventListener(visibilityChange, function() {    if(document_hidden != document[hidden]) {      if(document[hidden]) {        // Document hidden      } else {        // Document shown      }      document_hidden = document[hidden];    }  });});

Update: The example above used to have prefixed properties for Gecko and WebKit browsers, but I removed that implementation because these browsers have been offering Page Visibility API without a prefix for a while now. I kept Microsoft specific prefix in order to stay compatible with IE10.