我的代码

let browser_active = ((typeof document.hasFocus != 'undefined' ? document.hasFocus() : 1) ? 1 : 0);
if (!browser_active) {
 // active
} 

有3种典型的方法来确定用户是否可以看到HTML页面，但是没有一种方法是完美的:

The W3C Page Visibility API is supposed to do this (supported since: Firefox 10, MSIE 10, Chrome 13). However, this API only raises events when the browser tab is fully overriden (e.g. when the user changes from one tab to another one). The API does not raise events when the visibility cannot be determined with 100% accuracy (e.g. Alt+Tab to switch to another application). Using focus/blur based methods gives you a lot of false positive. For example, if the user displays a smaller window on top of the browser window, the browser window will lose the focus (onblur raised) but the user is still able to see it (so it still need to be refreshed). See also http://javascript.info/tutorial/focus Relying on user activity (mouse move, clicks, key typed) gives you a lot of false positive too. Think about the same case as above, or a user watching a video.

为了改善上面描述的不完美行为，我使用了三种方法的组合:W3C可视性API，然后是焦点/模糊和用户活动方法，以降低假阳性率。这允许管理以下事件:

将浏览器选项卡更改为另一个选项卡(100%的准确性，感谢W3C页面可见性API) 页面可能被另一个窗口隐藏，例如，由于Alt+Tab(概率=不是100%准确) 用户的注意力可能不会集中在HTML页面上(概率=不是100%准确)

This is how it works: when the document lose the focus, the user activity (such as mouse move) on the document is monitored in order to determine if the window is visible or not. The page visibility probability is inversely proportional to the time of the last user activity on the page: if the user makes no activity on the document for a long time, the page is most probably not visible. The code below mimics the W3C Page Visibility API: it behaves the same way but has a small false positive rate. It has the advantage to be multibrowser (tested on Firefox 5, Firefox 10, MSIE 9, MSIE 7, Safari 5, Chrome 9).

    <div id="x"></div>
     
    <script>
    /**
    Registers the handler to the event for the given object.
    @param obj the object which will raise the event
    @param evType the event type: click, keypress, mouseover, ...
    @param fn the event handler function
    @param isCapturing set the event mode (true = capturing event, false = bubbling event)
    @return true if the event handler has been attached correctly
    */
    function addEvent(obj, evType, fn, isCapturing){
      if (isCapturing==null) isCapturing=false; 
      if (obj.addEventListener){
        // Firefox
        obj.addEventListener(evType, fn, isCapturing);
        return true;
      } else if (obj.attachEvent){
        // MSIE
        var r = obj.attachEvent('on'+evType, fn);
        return r;
      } else {
        return false;
      }
    }
     
    // register to the potential page visibility change
    addEvent(document, "potentialvisilitychange", function(event) {
      document.getElementById("x").innerHTML+="potentialVisilityChange: potentialHidden="+document.potentialHidden+", document.potentiallyHiddenSince="+document.potentiallyHiddenSince+" s<br>";
    });
     
    // register to the W3C Page Visibility API
    var hidden=null;
    var visibilityChange=null;
    if (typeof document.mozHidden !== "undefined") {
      hidden="mozHidden";
      visibilityChange="mozvisibilitychange";
    } else if (typeof document.msHidden !== "undefined") {
      hidden="msHidden";
      visibilityChange="msvisibilitychange";
    } else if (typeof document.webkitHidden!=="undefined") {
      hidden="webkitHidden";
      visibilityChange="webkitvisibilitychange";
    } else if (typeof document.hidden !=="hidden") {
      hidden="hidden";
      visibilityChange="visibilitychange";
    }
    if (hidden!=null && visibilityChange!=null) {
      addEvent(document, visibilityChange, function(event) {
        document.getElementById("x").innerHTML+=visibilityChange+": "+hidden+"="+document[hidden]+"<br>";
      });
    }
     
     
    var potentialPageVisibility = {
      pageVisibilityChangeThreshold:3*3600, // in seconds
      init:function() {
        function setAsNotHidden() {
          var dispatchEventRequired=document.potentialHidden;
          document.potentialHidden=false;
          document.potentiallyHiddenSince=0;
          if (dispatchEventRequired) dispatchPageVisibilityChangeEvent();
        }
     
        function initPotentiallyHiddenDetection() {
          if (!hasFocusLocal) {
            // the window does not has the focus => check for  user activity in the window
            lastActionDate=new Date();
            if (timeoutHandler!=null) {
              clearTimeout(timeoutHandler);
            }
            timeoutHandler = setTimeout(checkPageVisibility, potentialPageVisibility.pageVisibilityChangeThreshold*1000+100); // +100 ms to avoid rounding issues under Firefox
          }
        }
     
        function dispatchPageVisibilityChangeEvent() {
          unifiedVisilityChangeEventDispatchAllowed=false;
          var evt = document.createEvent("Event");
          evt.initEvent("potentialvisilitychange", true, true);
          document.dispatchEvent(evt);
        }
     
        function checkPageVisibility() {
          var potentialHiddenDuration=(hasFocusLocal || lastActionDate==null?0:Math.floor((new Date().getTime()-lastActionDate.getTime())/1000));
                                        document.potentiallyHiddenSince=potentialHiddenDuration;
          if (potentialHiddenDuration>=potentialPageVisibility.pageVisibilityChangeThreshold && !document.potentialHidden) {
            // page visibility change threshold raiched => raise the even
            document.potentialHidden=true;
            dispatchPageVisibilityChangeEvent();
          }
        }
                            
        var lastActionDate=null;
        var hasFocusLocal=true;
        var hasMouseOver=true;
        document.potentialHidden=false;
        document.potentiallyHiddenSince=0;
        var timeoutHandler = null;
     
        addEvent(document, "pageshow", function(event) {
          document.getElementById("x").innerHTML+="pageshow/doc:<br>";
        });
        addEvent(document, "pagehide", function(event) {
          document.getElementById("x").innerHTML+="pagehide/doc:<br>";
        });
        addEvent(window, "pageshow", function(event) {
          document.getElementById("x").innerHTML+="pageshow/win:<br>"; // raised when the page first shows
        });
        addEvent(window, "pagehide", function(event) {
          document.getElementById("x").innerHTML+="pagehide/win:<br>"; // not raised
        });
        addEvent(document, "mousemove", function(event) {
          lastActionDate=new Date();
        });
        addEvent(document, "mouseover", function(event) {
          hasMouseOver=true;
          setAsNotHidden();
        });
        addEvent(document, "mouseout", function(event) {
          hasMouseOver=false;
          initPotentiallyHiddenDetection();
        });
        addEvent(window, "blur", function(event) {
          hasFocusLocal=false;
          initPotentiallyHiddenDetection();
        });
        addEvent(window, "focus", function(event) {
          hasFocusLocal=true;
          setAsNotHidden();
        });
        setAsNotHidden();
      }
    }
     
    potentialPageVisibility.pageVisibilityChangeThreshold=4; // 4 seconds for testing
    potentialPageVisibility.init();
    </script>

由于目前还没有有效的跨浏览器解决方案，所以在禁用网站上的周期性活动时最好三思而后行。

这在chrome 67和firefox 67上都适用，

if(!document.hasFocus()) {
    // do stuff
}

从最初编写这个答案开始，由于W3C，一个新的规范已经达到了推荐状态。页面可见性API(在MDN上)现在允许我们更准确地检测页面何时对用户隐藏。

document.addEventListener("visibilitychange", onchange);

当前浏览器支持:

铬13 + Internet Explorer 10+ Firefox 10 + Opera 12.10+[阅读笔记]

下面的代码在不兼容的浏览器中退回到不太可靠的模糊/聚焦方法:

(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";
  }

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

ie9及以下版本需要onfocusin和onfocusout，而所有其他都使用onfocus和onblur，除了iOS，它使用onpageshow和onpagehide。

Chromium团队目前正在开发空闲检测API。从Chrome 88开始，它就可以作为原始试用版使用，这已经是该功能的第2个原始试用版了。早期的版本是从Chrome 84到Chrome 86。

它也可以通过一个标志来启用:

启用通过chrome://flags 要在本地使用空闲检测API进行实验，而不需要 源试用令牌，启用 #enable-experimental-web-platform-features标记 chrome: / /旗帜。

一个演示可以在这里找到:

https://idle-detection.glitch.me/

但必须指出的是，这个API是基于权限的(因为它应该是，否则这可能被滥用来监视用户的行为!)。

稍微复杂一点的方法是使用setInterval()检查鼠标位置并与上次检查进行比较。如果鼠标在一段时间内没有移动，则用户可能处于空闲状态。

这有一个额外的好处，可以告诉用户是否空闲，而不仅仅是检查窗口是否处于活动状态。

正如许多人指出的那样，这并不总是一种检查用户或浏览器窗口是否空闲的好方法，因为用户甚至可能没有使用鼠标或正在观看视频或类似的内容。我只是建议一种检查空闲状态的方法。