Check if my website is open in another tab

Question

I want to check with JavaScript if the user has already opened my website in another tab in their browser.

It seems I cannot do that with pagevisibility...

The only way I see is to use WebSocket based on a session cookie, and check if the client has more than one socket. But by this way, from current tab, I have to ask my server if this user has a tab opened right next to their current browser tab. It is a little far-fetched!

Maybe with localstorage?

Answer 1

The shorter version with localStorage and Storage listener

<script type="text/javascript">
        // Broadcast that you're opening a page.
        localStorage.openpages = Date.now();
        var onLocalStorageEvent = function(e){
            if(e.key == "openpages"){
                // Listen if anybody else is opening the same page!
                localStorage.page_available = Date.now();
            }
            if(e.key == "page_available"){
                alert("One more page already open");
            }
        };
        window.addEventListener('storage', onLocalStorageEvent, false);
</script>

Update:

• Works on page crash as well.
• Stimulate page crash in chrome: chrome://inducebrowsercrashforrealz

Live demo

Answer 2

Using local storage I created a simple demo that should accomplish what your looking to do. Basically, it simply maintains a count of currently opened windows. When the window is closed the unload events fire and remove it from the total window count.

When you first look at it, you may think there's more going on than there really is. Most of it was a shotty attempt to add logic into who was the "main" window, and who should take over as the "main" window as you closed children. (Hence the setTimeout calls to recheck if it should be promoted to a main window) After some head scratching, I decided it would take too much time to implement and was outside the scope of this question. However, if you have two windows open (Main, and Child) and you close the Main, the child will be promoted to a main.

For the most part you should be able to get the general idea of whats going on and use it for your own implementation.

See it all in action here: http://jsbin.com/mipanuro/1/edit

Oh yeah, to actually see it in action... Open the link in multiple windows. :)

Update:

I've made the necessary changes to have the the local storage maintain the "main" window. As you close tabs child windows can then become promoted to a main window. There are two ways to control the "main" window state through a parameter passed to the constructor of WindowStateManager. This implementation is much nicer than my previous attempt.

JavaScript:

// noprotect

var statusWindow = document.getElementById('status');

(function (win)
{
    //Private variables
    var _LOCALSTORAGE_KEY = 'WINDOW_VALIDATION';
    var RECHECK_WINDOW_DELAY_MS = 100;
    var _initialized = false;
    var _isMainWindow = false;
    var _unloaded = false;
    var _windowArray;
    var _windowId;
    var _isNewWindowPromotedToMain = false;
    var _onWindowUpdated;

    
    function WindowStateManager(isNewWindowPromotedToMain, onWindowUpdated)
    {
        //this.resetWindows();
        _onWindowUpdated = onWindowUpdated;
        _isNewWindowPromotedToMain = isNewWindowPromotedToMain;
        _windowId = Date.now().toString();

        bindUnload();

        determineWindowState.call(this);

        _initialized = true;

        _onWindowUpdated.call(this);
    }

    //Determine the state of the window 
    //If its a main or child window
    function determineWindowState()
    {
        var self = this;
        var _previousState = _isMainWindow;

        _windowArray = localStorage.getItem(_LOCALSTORAGE_KEY);

        if (_windowArray === null || _windowArray === "NaN")
        {
            _windowArray = [];
        }
        else
        {
            _windowArray = JSON.parse(_windowArray);
        }

        if (_initialized)
        {
            //Determine if this window should be promoted
            if (_windowArray.length <= 1 ||
               (_isNewWindowPromotedToMain ? _windowArray[_windowArray.length - 1] : _windowArray[0]) === _windowId)
            {
                _isMainWindow = true;
            }
            else
            {
                _isMainWindow = false;
            }
        }
        else
        {
            if (_windowArray.length === 0)
            {
                _isMainWindow = true;
                _windowArray[0] = _windowId;
                localStorage.setItem(_LOCALSTORAGE_KEY, JSON.stringify(_windowArray));
            }
            else
            {
                _isMainWindow = false;
                _windowArray.push(_windowId);
                localStorage.setItem(_LOCALSTORAGE_KEY, JSON.stringify(_windowArray));
            }
        }

        //If the window state has been updated invoke callback
        if (_previousState !== _isMainWindow)
        {
            _onWindowUpdated.call(this);
        }

        //Perform a recheck of the window on a delay
        setTimeout(function()
                   {
                     determineWindowState.call(self);
                   }, RECHECK_WINDOW_DELAY_MS);
    }

    //Remove the window from the global count
    function removeWindow()
    {
        var __windowArray = JSON.parse(localStorage.getItem(_LOCALSTORAGE_KEY));
        for (var i = 0, length = __windowArray.length; i < length; i++)
        {
            if (__windowArray[i] === _windowId)
            {
                __windowArray.splice(i, 1);
                break;
            }
        }
        //Update the local storage with the new array
        localStorage.setItem(_LOCALSTORAGE_KEY, JSON.stringify(__windowArray));
    }

    //Bind unloading events  
    function bindUnload()
    {
        win.addEventListener('beforeunload', function ()
        {
            if (!_unloaded)
            {
                removeWindow();
            }
        });
        win.addEventListener('unload', function ()
        {
            if (!_unloaded)
            {
                removeWindow();
            }
        });
    }

    WindowStateManager.prototype.isMainWindow = function ()
    {
        return _isMainWindow;
    };

    WindowStateManager.prototype.resetWindows = function ()
    {
        localStorage.removeItem(_LOCALSTORAGE_KEY);
    };

    win.WindowStateManager = WindowStateManager;
})(window);

var WindowStateManager = new WindowStateManager(false, windowUpdated);

function windowUpdated()
{
    //"this" is a reference to the WindowStateManager
    statusWindow.className = (this.isMainWindow() ? 'main' : 'child');
}
//Resets the count in case something goes wrong in code
//WindowStateManager.resetWindows()

HTML:

<!DOCTYPE html>
<html>
<head>
  <meta charset="utf-8">
  <title>JS Bin</title>
</head>
<body>
  <div id='status'> 
    <span class='mainWindow'>Main Window</span>
    <span class='childWindow'>Child Window</span>
  </div>
</body>
</html>

CSS:

#status
{
  display:table;
  width:100%;
  height:500px;
  border:1px solid black;
}
span
{
  vertical-align:middle;
  text-align:center; 
  margin:0 auto;
  font-size:50px;
  font-family:arial;
  color:#ba3fa3;  
  display:none;
}

#status.main .mainWindow,
#status.child .childWindow
{
  display:table-cell;
}

.mainWindow
{
  background-color:#22d86e;
}
.childWindow
{
  background-color:#70aeff;
}

Answer 3

(2021) You can use BroadcastChannel to communicate between tabs of the same origin.

For example, put the following at the top level of your js code, then test by opening 2 tabs:

const bc = new BroadcastChannel("my-awesome-site");

bc.onmessage = (event) => {
  if (event.data === `Am I the first?`) {
    bc.postMessage(`No you're not.`);
    alert(`Another tab of this site just got opened`);
  }
  if (event.data === `No you're not.`) {
    alert(`An instance of this site is already running`);
  }
};

bc.postMessage(`Am I the first?`);

Answer 4

I know it is late, but maybe help someone

This snippet of code, will detect how many tabs are open and how many are active (visible) and if none of tabs is active, it will choose last opened tab, as active one.

This code will handle windows/tab crash too and it will refresh the count at crash.

Because localStorage is not supported on Stack Overflow currently, please test here.

<html>
<body>
Open in several tabs or windows
<div id="holder_element"></div>

<script type="text/javascript">
    //localStorage.clear();
    manage_crash();
    
    //Create a windows ID for each windows that is oppened
    var current_window_id = Date.now() + "";//convert to string
    var time_period = 3000;//ms
    
    //Check to see if PageVisibility API is supported or not
    var PV_API = page_visibility_API_check();
    
    /************************
    ** PAGE VISIBILITY API **
    *************************/
    function page_visibility_API_check ()
    {
        var page_visibility_API = false;
        var visibility_change_handler = false;
        if ('hidden' in document)
        {
            page_visibility_API = 'hidden';
            visibility_change_handler = 'visibilitychange';
        }
        else
        {
            var prefixes = ['webkit','moz','ms','o'];
            //loop over all the known prefixes
            for (var i = 0; i < prefixes.length; i++){
                if ((prefixes[i] + 'Hidden') in document)
                {
                    page_visibility_API = prefixes[i] + 'Hidden';
                    visibility_change_handler = prefixes[i] + 'visibilitychange';
                }
            }
        }
        
        if (!page_visibility_API)
        {
            //PageVisibility API is not supported in this device
            return page_visibility_API;
        }
        
        return {"hidden": page_visibility_API, "handler": visibility_change_handler};
    }
    
    if (PV_API)
    {
        document.addEventListener(PV_API.handler, function(){
            //console.log("current_window_id", current_window_id, "document[PV_API.hidden]", document[PV_API.hidden]);
            if (document[PV_API.hidden])
            {
                //windows is hidden now
                remove_from_active_windows(current_window_id);
                //skip_once = true;
            }
            else
            {
                //windows is visible now
                //add_to_active_windows(current_window_id);
                //skip_once = false;
                check_current_window_status ();
            }
        }, false);
    }
    
    /********************************************
    ** ADD CURRENT WINDOW TO main_windows LIST **
    *********************************************/
    add_to_main_windows_list(current_window_id);
    //update active_window to current window
    localStorage.active_window = current_window_id;
    
    /**************************************************************************
    ** REMOVE CURRENT WINDOWS FROM THE main_windows LIST ON CLOSE OR REFRESH **
    ***************************************************************************/
    window.addEventListener('beforeunload', function ()
    {
        remove_from_main_windows_list(current_window_id);
    });
    
    /*****************************
    ** ADD TO main_windows LIST **
    ******************************/
    function add_to_main_windows_list(window_id)
    {
        var temp_main_windows_list = get_main_windows_list();
        var index = temp_main_windows_list.indexOf(window_id);
        
        if (index < 0)
        {
            //this windows is not in the list currently
            temp_main_windows_list.push(window_id);
        }
        
        localStorage.main_windows = temp_main_windows_list.join(",");
        
        return temp_main_windows_list;
    }
    
    /**************************
    ** GET main_windows LIST **
    ***************************/
    function get_main_windows_list()
    {
        var temp_main_windows_list = [];
        if (localStorage.main_windows)
        {
            temp_main_windows_list = (localStorage.main_windows).split(",");
        }
        
        return temp_main_windows_list;
    }
    
    /**********************************************
    ** REMOVE WINDOWS FROM THE main_windows LIST **
    ***********************************************/
    function remove_from_main_windows_list(window_id)
    {
        var temp_main_windows_list = [];
        if (localStorage.main_windows)
        {
            temp_main_windows_list = (localStorage.main_windows).split(",");
        }
        
        var index = temp_main_windows_list.indexOf(window_id);
        if (index > -1) {
            temp_main_windows_list.splice(index, 1);
        }
        
        localStorage.main_windows = temp_main_windows_list.join(",");
        
        //remove from active windows too
        remove_from_active_windows(window_id);
        
        return temp_main_windows_list;
    }
    
    /**************************
    ** GET active_windows LIST **
    ***************************/
    function get_active_windows_list()
    {
        var temp_active_windows_list = [];
        if (localStorage.actived_windows)
        {
            temp_active_windows_list = (localStorage.actived_windows).split(",");
        }
        
        return temp_active_windows_list;
    }
    
    /*************************************
    ** REMOVE FROM actived_windows LIST **
    **************************************/
    function remove_from_active_windows(window_id)
    {
        var temp_active_windows_list = get_active_windows_list();
        
        var index = temp_active_windows_list.indexOf(window_id);
        if (index > -1) {
            temp_active_windows_list.splice(index, 1);
        }
        
        localStorage.actived_windows = temp_active_windows_list.join(",");
        
        return temp_active_windows_list;
    }
    
    /********************************
    ** ADD TO actived_windows LIST **
    *********************************/
    function add_to_active_windows(window_id)
    {
        var temp_active_windows_list = get_active_windows_list();
        
        var index = temp_active_windows_list.indexOf(window_id);
        
        if (index < 0)
        {
            //this windows is not in active list currently
            temp_active_windows_list.push(window_id);
        }

        localStorage.actived_windows = temp_active_windows_list.join(",");
        
        return temp_active_windows_list;
    }
    
    /*****************
    ** MANAGE CRASH **
    ******************/
    //If the last update didn't happened recently (more than time_period*2)
    //we will clear saved localStorage's data and reload the page
    function manage_crash()
    {
        if (localStorage.last_update)
        {
            if (parseInt(localStorage.last_update) + (time_period * 2) < Date.now())
            {
                //seems a crash came! who knows!?
                //localStorage.clear();
                localStorage.removeItem('main_windows');
                localStorage.removeItem('actived_windows');
                localStorage.removeItem('active_window');
                localStorage.removeItem('last_update');
                location.reload();
            }
        }
    }
    
    /********************************
    ** CHECK CURRENT WINDOW STATUS **
    *********************************/
    function check_current_window_status(test)
    {
        manage_crash();
        
        if (PV_API)
        {
            var active_status = "Inactive";
            var windows_list = get_main_windows_list();
            
            var active_windows_list = get_active_windows_list();
            
            if (windows_list.indexOf(localStorage.active_window) < 0)
            {
                //last actived windows is not alive anymore!
                //remove_from_main_windows_list(localStorage.active_window);
                
                //set the last added window, as active_window
                localStorage.active_window = windows_list[windows_list.length - 1];
            }
            
            if (! document[PV_API.hidden])
            {
                //Window's page is visible
                localStorage.active_window = current_window_id;
            }
            
            if (localStorage.active_window == current_window_id)
            {
                active_status = "Active";
            }
            
            if (active_status == "Active")
            {
                active_windows_list = add_to_active_windows(current_window_id);
            }
            else
            {
                active_windows_list = remove_from_active_windows(current_window_id);
            }
            
            console.log(test, active_windows_list);
            
            var element_holder = document.getElementById("holder_element");
            element_holder.insertAdjacentHTML("afterbegin", "<div>"+element_holder.childElementCount+") Current Windows is "+ active_status +"&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;"+active_windows_list.length+" window(s) is visible and active of "+ windows_list.length +" windows</div>");
        }
        else
        {
            console.log("PageVisibility API is not supported :(");
            //our INACTIVE pages, will remain INACTIVE forever, you need to make some action in this case!
        }
        
        localStorage.last_update = Date.now();
    }
    
    //check storage continuously
    setInterval(function(){
        check_current_window_status ();
    }, time_period);
    
    //initial check
    check_current_window_status ();
</script>
</body>
</html>