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Presence in Express

Three ways to show people: a presence room lists who is in it to everyone in it (who is in the shop, who is viewing a document). A count says how many, at any size. And who is online is known across your whole app, for a dot on every avatar.

The browsers of Ann, Ben and Cara, each listing the three of them in the shop now, with their roles from the info of each member

A presence room​

// Who is in the shop: everyone signed in, with their name and role.
realtime.room( 'shop', { presence: true }, async ( user ) => {
    const person = user === null ? null : await db.users.find( user );
    return person ? { info: { name: person.name, role: person.role } } : false;
} );
  • info is what the others see of the member: a name, a role, anything small (up to 4 KB). It is sealed with the room key.
  • Up to 1,000 members are listed in full, with join and leave. Past that, the room counts them, and members() pages through them, up to 100,000.
const shop = rt.join( 'shop' );
const draw = () => list( [ ...shop.members ] );        // [ [ id, info ], … ]
shop.on( 'joined', draw );                             // the members as the page joins
shop.on( 'join', ( { id, info } ) => draw() );
shop.on( 'leave', ( { id } ) => draw() );

A user is a member once, however many tabs and devices they have in the room, and leaves when the last one does.

Counting​

count: true gives a room a live count, without a list:

realtime.room( 'product:{id}', { public: true, count: true } );
const product = rt.join( 'product:7' );
product.on( 'count', ( n ) => showLooking( n ) );   // at most once a second

A presence room counts too. product.count holds the latest.

Who is online, across your app​

Every page whose user your server vouched for makes that user online. They go offline 10 seconds after their last page closes, so a reload does not flicker.

rt.online.watch( [ 34, 43 ] ).on( 'change', ( { id, online, at } ) => dot( id, online ) );
rt.online.has( 34 );          // true or false, for a user watched
rt.online.lastSeen( 43 );     // when, in ms, for one offline
rt.online.on( 'count', ( n ) => showOnline( n ) );   // how many are online, live
  • A page watches up to 1,000 users, and gets their status now and every change.
  • Your server asks too: await realtime.online.has( 42 ), .count(), .list().
  • Hiding: a user who chose not to show their status is never online to anyone:
const realtime = createRealtime( {
    // …
    hidden: async ( user ) => ( await db.users.find( user ) )?.hideStatus === true,
} );

Ready-made: who is online​

The Better Messages list of members, on a presence room, with a call button for each of the others. It is one element:

<wordplus-online room="shop" title="In the shop now" call="support:{pair}" type="video"></wordplus-online>
<wordplus-online-count room="product:7"></wordplus-online-count>
await rt.callScreen();   // loads the elements and the call screen, rt.ui() the elements without calls
  • call names the call the button of each row places: {pair} is the two user ids in order (support:34:42), {me} and {id} each one. Without it, the rows have no button.
  • type is video, audio, or both: type="audio video".
  • Names and pictures come from the member info, then from your directory.
  • Its look is that of Better Messages, in a shadow root: your page styles do not reach in, and its colours are CSS custom properties your page sets.

More, with PHP and Python side by side: presence in depth.