Communication between tabs or windows

Question

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 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.

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

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 4KB.

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.

Edit 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.

Answer 1

I created a module that works equal to the official Broadcastchannel but has fallbacks based on localstorage, indexeddb and unix-sockets. This makes sure it always works even with Webworkers or NodeJS. See pubkey:BroadcastChannel

Answer 2

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

---

There are different approaches and each one has its own advantages and disadvantages. Lets 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 5120KB (5MB which equals 2.5 Million chars on Chrome) is the default storage size for an entire domain. This gives you considerably more space to work with than a typical 4KB 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 4K 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 max 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.

Answer 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);
    }
}

Answer 4

There's a tiny open-source component to sync/communicate between tabs/windows of the same origin (disclaimer - I'm one of the contributors!) based around localStorage.

TabUtils.BroadcastMessageToAllTabs("eventName", eventDataString);

TabUtils.OnBroadcastMessage("eventName", function (eventDataString) {
    DoSomething();
});

TabUtils.CallOnce("lockname", function () {
    alert("I run only once across multiple tabs");
});

https://github.com/jitbit/TabUtils

P.S. I took the liberty to recommend it here since most of the "lock/mutex/sync" components fail on websocket connections when events happen almost simultaneously

Answer 5

I wrote an article on this on my blog: http://www.ebenmonney.com/blog/how-to-implement-remember-me-functionality-using-token-based-authentication-and-localstorage-in-a-web-application .

Using a library I created storageManager you can achieve this as follows:

storageManager.savePermanentData('data', 'key'): //saves permanent data
storageManager.saveSyncedSessionData('data', 'key'); //saves session data to all opened tabs
storageManager.saveSessionData('data', 'key'); //saves session data to current tab only
storageManager.getData('key'); //retrieves data

There are other convenient methods as well to handle other scenarios as well

Answer 6

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.

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