Communication between tabs or windows

I was searching for a way how to communicate between multiple tabs or windows in a browser (on the same domain, not CORS) without leaving traces. There were several solutions:

1. using the window object
2. postMessage
3. cookies
4. localStorage

The first is probably the worst solution - you need to open a window from your current window and then you can communicate only as long as you keep the windows open. If you reload the page in any of the windows, you most likely lost the communication.

The second approach, using postMessage, probably enables cross-origin communication, but it suffers the same problem as the first approach. You need to maintain a window object.

The third way, using cookies, store some data in the browser, which can effectively look like sending a message to all windows on the same domain, but the problem is that you can never know if all tabs read the "message" already or not before cleaning up. You have to implement some sort of timeout to read the cookie periodically. Furthermore you are limited by maximum cookie length, which is 4 KB.

The fourth solution, using localStorage, seemed to overcome the limitations of cookies, and it can be even listen-to using events. How to use it is described in the accepted answer.

In 2018, the accepted answer still works, but there is a newer solution for modern browsers, to use BroadcastChannel. See the other answer for a simple example describing how to easily transmit message between tabs by using BroadcastChannel.

Solution 1:

You may better use BroadcastChannel for this purpose. See other answers below. Yet if you still prefer to use localstorage for communication between tabs, do it this way:

In order to get notified when a tab sends a message to other tabs, you simply need to bind on 'storage' event. In all tabs, do this:

$(window).on('storage', message_receive);

The function message_receive will be called every time you set any value of localStorage in any other tab. The event listener contains also the data newly set to localStorage, so you don't even need to parse localStorage object itself. This is very handy because you can reset the value just right after it was set, to effectively clean up any traces. Here are functions for messaging:

// use local storage for messaging. Set message in local storage and clear it right away
// This is a safe way how to communicate with other tabs while not leaving any traces
//
function message_broadcast(message)
{
    localStorage.setItem('message',JSON.stringify(message));
    localStorage.removeItem('message');
}


// receive message
//
function message_receive(ev)
{
    if (ev.originalEvent.key!='message') return; // ignore other keys
    var message=JSON.parse(ev.originalEvent.newValue);
    if (!message) return; // ignore empty msg or msg reset

    // here you act on messages.
    // you can send objects like { 'command': 'doit', 'data': 'abcd' }
    if (message.command == 'doit') alert(message.data);

    // etc.
}

So now once your tabs bind on the onstorage event, and you have these two functions implemented, you can simply broadcast a message to other tabs calling, for example:

message_broadcast({'command':'reset'})

Remember that sending the exact same message twice will be propagated only once, so if you need to repeat messages, add some unique identifier to them, like

message_broadcast({'command':'reset', 'uid': (new Date).getTime()+Math.random()})

Also remember that the current tab which broadcasts the message doesn't actually receive it, only other tabs or windows on the same domain.

You may ask what happens if the user loads a different webpage or closes his tab just after the setItem() call before the removeItem(). Well, from my own testing the browser puts unloading on hold until the entire function message_broadcast() is finished. I tested to put some very long for() cycle in there and it still waited for the cycle to finish before closing. If the user kills the tab just in-between, then the browser won't have enough time to save the message to disk, thus this approach seems to me like safe way how to send messages without any traces.

Solution 2:

There is a modern API dedicated for this purpose - Broadcast Channel

It is as easy as:

var bc = new BroadcastChannel('test_channel');

bc.postMessage('This is a test message.'); /* send */

bc.onmessage = function (ev) { console.log(ev); } /* receive */

There is no need for the message to be just a DOMString. Any kind of object can be sent.

Probably, apart from API cleanness, it is the main benefit of this API - no object stringification.

It is currently supported only in Chrome and Firefox, but you can find a polyfill that uses localStorage.

Solution 3:

For those searching for a solution not based on jQuery, this is a plain JavaScript version of the solution provided by Thomas M:

window.addEventListener("storage", message_receive);

function message_broadcast(message) {
    localStorage.setItem('message',JSON.stringify(message));
}

function message_receive(ev) {
    if (ev.key == 'message') {
        var message=JSON.parse(ev.newValue);
    }
}

Solution 4:

Checkout AcrossTabs - Easy communication between cross-origin browser tabs. It uses a combination of the postMessage and sessionStorage APIs to make communication much easier and reliable.

There are different approaches and each one has its own advantages and disadvantages. Let’s discuss each:

1. LocalStorage

   Pros:

   1. Web storage can be viewed simplistically as an improvement on cookies, providing much greater storage capacity. If you look at the Mozilla source code we can see that 5120 KB (5 MB which equals 2.5 million characters on Chrome) is the default storage size for an entire domain. This gives you considerably more space to work with than a typical 4 KB cookie.
   2. The data is not sent back to the server for every HTTP request (HTML, images, JavaScript, CSS, etc.) - reducing the amount of traffic between client and server.
   3. The data stored in localStorage persists until explicitly deleted. Changes made are saved and available for all current and future visits to the site.

   Cons:

   1. It works on same-origin policy. So, data stored will only be able available on the same origin.

2. Cookies

   Pros:

   1. Compared to others, there's nothing AFAIK.

   Cons:

   1. The 4 KB limit is for the entire cookie, including name, value, expiry date, etc. To support most browsers, keep the name under 4000 bytes, and the overall cookie size under 4093 bytes.
   2. The data is sent back to the server for every HTTP request (HTML, images, JavaScript, CSS, etc.) - increasing the amount of traffic between client and server.

   Typically, the following are allowed:

   • 300 cookies in total
   • 4096 bytes per cookie
   • 20 cookies per domain
   • 81920 bytes per domain (given 20 cookies of the maximum size 4096 = 81920 bytes.)

3. sessionStorage

   Pros:

   1. It is similar to localStorage.
   2. Changes are only available per window (or tab in browsers like Chrome and Firefox). Changes made are saved and available for the current page, as well as future visits to the site on the same window. Once the window is closed, the storage is deleted

   Cons:

   1. The data is available only inside the window/tab in which it was set.
   2. The data is not persistent, i.e., it will be lost once the window/tab is closed.
   3. Like localStorage, tt works on same-origin policy. So, data stored will only be able available on the same origin.

4. PostMessage

   Pros:

   1. Safely enables cross-origin communication.
   2. As a data point, the WebKit implementation (used by Safari and Chrome) doesn't currently enforce any limits (other than those imposed by running out of memory).

   Cons:

   1. Need to open a window from the current window and then can communicate only as long as you keep the windows open.
   2. Security concerns - Sending strings via postMessage is that you will pick up other postMessage events published by other JavaScript plugins, so be sure to implement a targetOrigin and a sanity check for the data being passed on to the messages listener.

5. A combination of PostMessage + SessionStorage

   Using postMessage to communicate between multiple tabs and at the same time using sessionStorage in all the newly opened tabs/windows to persist data being passed. Data will be persisted as long as the tabs/windows remain opened. So, even if the opener tab/window gets closed, the opened tabs/windows will have the entire data even after getting refreshed.

I have written a JavaScript library for this, named AcrossTabs which uses postMessage API to communicate between cross-origin tabs/windows and sessionStorage to persist the opened tabs/windows identity as long as they live.