Did you know you can send information between open browser tabs using JavaScript?

Let's say your user is viewing your site with multiple tabs and something happens one tab which you want to react to on the other tabs - you can do this using the Broadcast Channel API.

Before we start, I want to mention that this only works between browsing contexts on the same origin.

Browser Support

Please also check browser support before using this API. As of July 2020, it doesn't appear to be supported by Safari. Please see the Can I Use... link here

Sending Data

To send something to another tab, we need to first create a new BroadcastChannel instance. This is super easy, and looks like this:

    const channel = new BroadcastChannel("my-channel");

Notice how we passed in my-channel - this is the name of the channel which we are subscribing to. When subscribing to a channel, you're then able to post and receive messages from it.

Speaking of posting messages, let's do that right now:

    channel.postMessage("Hey, how's it going mate? I'm from a different tab!");

We can send multiple different kinds of objects with the postMessage method, for example:

    // array
    channel.postMessage([5, 10, 15, 20]);

    // object
    channel.postMessage({ name: "Dom", age: 30 });

    // blob
    channel.postMessage(new Blob(["sample text"], {
        type: "text/plain"
    }));

Receiving messages

Now, on the second tab, we can listen for and receive those messages. Open up a new tab (on the same origin, i.e. localhost) and include this code:

    // subscribe to the same channel, "my-channel"
    const channel = new BroadcastChannel("my-channel");

    channel.addEventListener("message", e => {
        console.log(e.data);
    });

Once this code is included, open up both the tabs, then refresh the original one (the one doing the posting), and you should see the data appearing in the console.

It's that easy! You simply listen for the message event and once you have it, access the data with the data property.

Video Tutorial

If you prefer a video version of the above tutorial, you can view it on my YouTube channel, dcode:

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