VirtualizedMessageList

The VirtualizedMessageList component renders a scrollable list of messages. It differs from the standard MessageList in that it handles UI virtualization by default. Virtualization is a technique used to emulate large lists of elements by rendering as few items as possible to maintain performance and decrease the load on the DOM, while preserving the user experience. These qualities make the VirtualizedMessageList ideal for livestream use cases, where a single channel may have thousands of currently active users.

Similar to the MessageList, the UI for each individual message is rendered conditionally based on its message.type value. The list renders date separators, message reactions, new message notifications, system messages, deleted messages, and standard messages containing text and/or attachments.

By default, the VirtualizedMessageList loads the most recent 25 messages held in the channel.state. More messages are fetched from the Stream Chat API and loaded into the DOM on scrolling up the list. The currently loaded messages are held in the ChannelStateContext and can be referenced with our custom hook.

const { messages } = useChannelStateContext();

The VirtualizedMessageList has no required props and by default pulls overridable data from the various contexts established in the Channel component. Customization of the messages rendered within the list is handled by the Message UI component.

Basic Usage

As a context consumer, the VirtualizedMessageList component must be rendered as a child of the Channel component. It can be rendered with or without a provided messages prop. Providing your own messages value will override the default value drawn from the ChannelStateContext.

Example 1 - without messages prop

<Chat client={client}>
  <ChannelList />
  <Channel>
    <VirtualizedMessageList />
    <MessageInput />
  </Channel>
</Chat>

Example 2 - with messages prop

const customMessages = [
  // array of messages
];

<Chat client={client}>
  <ChannelList />
  <Channel>
    <VirtualizedMessageList messages={customMessages} />
    <MessageInput />
  </Channel>
</Chat>;

Scroll Behavior Optimization

By default, the virtualized message list uses the latest message (which gets rendered first) in the list as the default item size. This can lead to inaccurate scroll thumb size or scroll jumps if the last item is unusually tall (for example, an attachment). To improve this behavior, set the defaultItemHeight property to a value close (or equal to) the height of the usual messages.

<VirtualizedMessageList messages={customMessages} defaultItemHeight={76} />

Message grouping

The VirtualizedMessageList internally creates a mapping of message id to a style group. There are 4 style groups - 'middle' | 'top' | 'bottom' | 'single'. Later these group style tags are incorporated into the class of the <li/> element that wraps the Message component. This allows us to style messages by their position in the message group. An example of such class is str-chat__li str-chat__li--bottom.

Props

additionalMessageInputProps

Additional props to be passed to the MessageInput component, available props. It is rendered when editing a message.

additionalVirtuosoProps

Additional props to be passed the underlying react-virtuoso virtualized list dependency.

closeReactionSelectorOnClick

If true, picking a reaction from the ReactionSelector component will close the selector.

customMessageRenderer

Custom message render function, overrides the default messageRenderer function defined in the component.

defaultItemHeight

If set, the default item height is used for the calculation of the total list height. Use if you expect messages with a lot of height variance.

disableDateSeparator

If true, disables the injection of date separator UI components.

groupStyles

Callback function to set group styles for each message.

hasMore

Whether the list has more items to load.

hideDeletedMessages

If true, removes the MessageDeleted components from the list.

hideNewMessageSeparator

If true, hides the DateSeparator component that renders when new messages are received in a channel that’s watched but not active.

loadingMore

Whether the list is currently loading more items.

loadMore

Function called when more messages are to be loaded, provide your own function to override the handler stored in context.

Message

Custom UI component to display an individual message.

messageLimit

The limit to use when paginating messages (the page size).

messages

The messages to render in the list, provide your own array to override the data stored in context.

overscan

The amount of extra content the list should render in addition to what’s necessary to fill in the viewport.

returnAllReadData

Keep track of read receipts for each message sent by the user. When disabled, only the last own message delivery / read status is rendered.

reviewProcessedMessage

Allows to review changes introduced to messages array on per message basis (for example date separator injection before a message). The array returned from the function is appended to the array of messages that are later rendered into React elements in the VirtualizedMessageList.

The function expects a single parameter, which is an object containing the following attributes:

• changes - array of messages representing the changes applied around a given processed message
• context - configuration params and information forwarded from processMessages
• index - index of the processed message in the original messages array
• messages - array of messages retrieved from the back-end
• processedMessages - newly built array of messages to be later rendered

The context has the following parameters:

• userId - the connected user ID;
• enableDateSeparator - flag determining whether the date separators will be injected Enable date separator
• hideDeletedMessages - flag determining whether deleted messages would be filtered out during the processing
• hideNewMessageSeparator - disables date separator display for unread incoming messages
• lastRead: Date when the channel has been last read. Sets the threshold after everything is considered unread

The example below demonstrates how the custom logic can decide, whether deleted messages should be rendered on a given date. In this example, the deleted messages neither the date separator would be rendered if all the messages on a given date are deleted.

const getMsgDate = (msg) =>
  (msg && msg.created_at && isDate(msg.created_at) && msg.created_at.toDateString()) || '';

const dateSeparatorFilter = (msg) => msg.customType !== 'message.date';

const msgIsDeleted = (msg) => msg.type === 'deleted';

const reviewProcessedMessage = ({ changes, index, messages, processedMessages }) => {
  const changesWithoutSeparator = changes.filter(dateSeparatorFilter);
  const dateSeparatorInjected = changesWithoutSeparator.length !== changes.length;
  const previousProcessedMessage = processedMessages[processedMessages.length - 1];
  const processedMessage = messages[index];
  const processedMessageDate = getMsgDate(processedMessage);

  if (dateSeparatorInjected) {
    if (!processedMessageDate) return changes;
    const followingMessages = messages.slice(index + 1);
    let allFollowingMessagesOnDateDeleted = false;

    for (const followingMsg of followingMessages) {
      const followingMsgDate = getMsgDate(followingMsg);
      if (followingMsgDate !== processedMessageDate) break;
      allFollowingMessagesOnDateDeleted = followingMsg.type === 'deleted';
    }

    return allFollowingMessagesOnDateDeleted ? [] : changes;
  } else if (
    msgIsDeleted(processedMessage) &&
    getMsgDate(previousProcessedMessage) !== getMsgDate(processedMessage)
  ) {
    return [];
  } else {
    return changes;
  }
};

scrollSeekPlaceHolder

Custom data passed to the list that determines when message placeholders should be shown during fast scrolling.

scrollToLatestMessageOnFocus

If true, the list will scroll to the latest message when the window regains focus.

shouldGroupByUser

If true, group messages belonging to the same user, otherwise show each message individually.

separateGiphyPreview

If true, the Giphy preview will render as a separate component above the MessageInput, rather than inline with the other messages in the list.

showUnreadNotificationAlways

The floating notification informing about unread messages will be shown when the UnreadMessagesSeparator is not visible. The default is false, that means the notification is shown only when viewing unread messages.

stickToBottomScrollBehavior

The scroll-to behavior when new messages appear. Use 'smooth' for regular chat channels and 'auto' (which results in instant scroll to bottom) if you expect high throughput.

sortReactionDetails

Comparator function to sort the list of reacted users. Should have the same signature as an array’s sort method.

sortReactions

Comparator function to sort reactions. Should have the same signature as an array’s sort method.

threadList

If true, indicates that the current VirtualizedMessageList component is part of a Thread.