如何判断当前窗口是否激活
http://stackoverflow.com/questions/1060008/is-there-a-way-to-detect-if-a-browser-window-is-not-currently-active
Current browser support:Chrome 13Internet Explorer 10Firefox 10Opera 12.10 [read notes]The following code makes use of the API, falling back to the less reliable blur/focus method in incompatible browsers.(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"; }})();