Data Sharing

Overview

The Channels API is accessible through the io.channels object.

See the JavaScript Channels example on GitHub.

Enabling Channels

Channels API

The Channels API is disabled by default. To enable it, set the channels property of the configuration object to true when initializing the io.Connect library:

const config = { channels: true };

const io = await IODesktop(config);

Channel Selector

To add the Channel Selector to your window, set "allowChannels" to true in your app definition file under the "details" top-level key:

{
    "title": "My App",
    "type": "window",
    "name": "my-app",
    "details": {
        "url": "https://my-app.com",
        "mode": "tab",
        "allowChannels": true
    }
}

In some cases, you may want to show the Channel Selector, but prevent the user from interacting with it. Set the "readOnlyChannelSelector" property to true under the "details" top-level key in your app definition file to achieve this:

{
    "title": "My App",
    "type": "window",
    "name": "my-app",
    "details": {
        "url": "https://my-app.com",
        "mode": "tab",
        "allowChannels": true,
        "readOnlyChannelSelector": true
    }
}

You can also set the Channel Selector as read-only on a global level from the system.json file under the "windows" top-level key:

{
    "windows": {
        "readOnlyChannelSelector": true
    }
}

⚠️ Note that the settings in your app definition file will override the global settings in the system.json file.

Current Channel

To get the name of the Channel to which your app is currently joined, use the my() method:

const myChannel = io.channels.my();

All Channels

To get a list of all Channel names, use the all() method:

const channelNames = await io.channels.all();

Add & Remove Channels

You can add or remove Channels at runtime. New dynamically added Channels won't be persisted after restart of io.Connect Desktop, unless they are recreated. A Channel that has been defined via configuration and is dynamically removed, will be restored on restart of io.Connect Desktop.

To add a Channel dynamically, use the add() method and pass a ChannelContext object as an argument:

const channelContext = {
    name: "Black",
    meta: { color: "black" },
    data: { io: 42 }
};

// Adding a new Channel.
const newChannelContext = await io.channels.add(channelContext);

To remove a Channel dynamically, use the remove() method and pass the name of the Channel to remove:

// Removing a Channel.
await io.channels.remove("Black");

Join & Leave Channels

To make your app join a Channel programmatically, use the join() method and specify the name of the Channel to join:

await io.channels.join("Red");

To leave the Channel your app is currently on, use the leave() method:

await io.channels.leave();

Retrieving Channel Context

To get the context of a Channel, use the get() method which accepts a Channel name as a required parameter:

const data = await io.channels.get("Green");

To get a list of the contexts of all Channels, use the list() method:

const channelContexts = await io.channels.list();

Subscribing for Channel Updates

To track the data in the current Channel, use the subscribe() method:

const handler = (data) => {
    // The callback will be invoked each time the data is updated.
    console.log(data);
};

// Subscribe for updates from the Channel your app is currently on.
io.channels.subscribe(handler);

The callback receives the data from the Channel and information about the current Channel.

The callback will be invoked in three cases:

  • the data property of the Channel you are currently on is updated;
  • the user has switched the Channel and you are receiving a snapshot of the new Channel data;
  • your app isn't joined to a Channel anymore (e.g., the user has deselected the current Channel). In this case, both data and channelInfo will be undefined;

To subscribe for updates from a specific Channel, use the subscribeFor() method:

const channelName = "Green";
const handler = (data) => {
    // The callback will be invoked each time the data is updated.
    console.log(data);
};

await io.channels.subscribeFor(channelName, handler);

The subscribeFor() method accepts a Channel name as a first parameter and a callback to handle Channel data updates.

Use the unsubscribe function returned by subscribe() and subscribeFor() to stop tracking updates of the Channel data:

const unsubscribe = await io.channels.subscribeFor(channelName, handler);

unsubscribe();

The handlers passed to the subscribe() and subscribeFor() methods also accept the Channel context and the updating Interop Instance peer ID as second and third arguments. The ChannelContext object contains the name of the Channel and the Channel meta data, and the updating Interop instance peer ID can be used to identify the app updating the Channel:

const handler = (data, channelContext, updaterID) => {
    // Check the current Interop instance peer ID against the updating instance ID.
    const isUpdatedByMe = io.interop.instance.peerId === updaterID;

    if(!isUpdatedByMe) {
        // Another app has published in the Channel.
        console.log(`App "${updaterID}" has published "${JSON.stringify(data)}" in Channel "${channelContext.name}".`);
    };
};

io.channels.subscribe(handler);

Publishing Data

To update the context of the Channel, use publish(). The publish() method accepts two parameters - data to publish (required) and an optional Channel ID specifying which Channel context to update. If you don't specify a Channel ID, the current Channel will be updated.

Updating the current Channel:

const data = { RIC: "VOD.L" };

await io.channels.publish(data);

Updating a specific Channel:

const data = { RIC: "VOD.L" };
const channelName = "Green";

await io.channels.publish(data, channelName);

А Channel may contain multiple data structures, e.g. RIC and clientId. When executing the code above, only the RIC field will be updated, leaving the other fields of the context unchanged.

The publish() method will throw an exception if you aren't on a Channel and try to publish data.

Channel Events

If you want to monitor how your app moves between Channels, subscribe for updates with the onChanged() method:

const handler = (newChannel) => {
    if (newChannel) {
        // Handle the case where you have switched to another Channel.
        console.log(newChannel);
    } else {
        // Handle the case where your app isn't joined to any Channel
        // (e.g., the user has deselected the current Channel).
        console.log("No Channel selected.")
    };
};

io.channels.onChanged(handler);

Reference

For a complete list of the available Channels API methods and properties, see the Channels API Reference Documentation.