添加事件监听

如需收到消息和事件通知，你需要先实现事件监听程序，然后订阅或者加入你想要接收消息或事件通知的频道。

添加事件监听

RTM 采用统一入口的方式处理消息和事件通知，每一种消息和事件通知都有对应的事件处理程序入口，你可以在其中实现自己的业务处理逻辑：

JavaScript

// Handle message event
rtm.addEventListener("message", event => {
    const channelType = event.channelType;      // The channel type need to be "STREAM", "MESSAGE" or "USER".
    const channelName = event.channelName;      // The name of the channel that this message comes from.
    const topic = event.topicName;              // (Stream channel only) The name of the topic that this message comes from.
    const messageType = event.messageType;      // The message type need to be "STRING" or "BINARY".
    const customType = event.customType;        // User defined type.
    const publisher = event.publisher;          // Message publisher.
    const message = event.message;              // Message payload.
    const timestamp = event.timestamp;          // Event timestamp
});
// Handle presence event
rtm.addEventListener("presence", event => {
    const action = event.eventType;             // Which action it is ,should be one of 'SNAPSHOT'、'INTERVAL'、'JOIN'、'LEAVE'、'TIMEOUT、'STATE_CHANGED'、'OUT_OF_SERVICE'.
    const channelType = event.channelType;      // Which channel type it is, Should be "STREAM", "MESSAGE" or "USER".
    const channelName = event.channelName;      // Which channel does this event come from
    const publisher = event.publisher;          // Who trigger this event
    const states = event.stateChanged;          // User state payload, only for stateChanged event
    const interval = event.interval;            // Interval payload, only for interval event
    const snapshot = event.snapshot;            // Snapshot payload, only for snapshot event
    const timestamp = event.timestamp;          // Event timestamp
});
// Handle topic event
rtm.addEventListener("topic", event => {
    const action = event.evenType;              // Which action it is ,should be one of 'SNAPSHOT'、'JOIN'、'LEAVE'.
    const channelName = event.channelName;      // Which channel does this event come from
    const publisher = event.userId;             // Who trigger this event
    const topicInfos = event.topicInfos;        // Topic information payload
    const totalTopics = event.totalTopics;      // How many topics
    const timestamp = event.timestamp;          // Event timestamp
});
// Handle storage event
rtm.addEventListener("storage", event => {
    const channelType = event.channelType;      // Which channel type it is, Should be "STREAM", "MESSAGE" or "USER".
    const channelName = event.channelName;      // Which channel does this event come from
    const publisher = event.publisher;          // Who trigger this event
    const storageType = event.storageType;      // Which category the event is, should be 'USER'、'CHANNEL'
    const action = event.eventType;             // Which action it is ,should be one of "SNAPSHOT"、"SET"、"REMOVE"、"UPDATE" or "NONE"
    const data = event.data;                    // 'USER_METADATA' or 'CHANNEL_METADATA' payload
    const timestamp = event.timestamp;          // Event timestamp
});
// Handle lock event
rtm.addEventListener("lock", event => {
    const channelType = event.channelType;      // Which channel type it is, Should be "STREAM", "MESSAGE" or "USER".
    const channelName = event.channelName;      // Which channel does this event come from
    const publisher = event.publisher;          // Who trigger this event
    const action = event.evenType;              // Which action it is ,should be one of 'SET'、'REMOVED'、'ACQUIRED'、'RELEASED'、'EXPIRED'、'SNAPSHOT'
    const lockName = event.lockName;            // Which lock it effect
    const ttl = event.ttl;                      // The ttl of this lock
    const snapshot = event.snapshot;            // Snapshot payload
    const owner = event.owner;                  // The owner of this lock
    const timestamp = event.timestamp;          // Event timestamp
});
// Handle connection state change event
rtm.addEventListener("status", event => {
    const currentState = event.state;                // Which connection state right now
    const changeReason = event.reason;                // Why trigger this event
    const timestamp = event.timestamp;          // Event timestamp
});
// Handle link state change event
rtm.addEventListener('linkState', event => {
    const currentState = event.currentState;
    const previousState = event.previousState;
    const serviceType = event.serviceType;
    const operation = event.operation;
    const reason = event.reason;
    const affectedChannels = event.affectedChannels;
    const timestamp = event.timestamp;
    const isResumed = event.isResumed;
});
// Handle token privilege will expire event
rtm.addEventListener("tokenPrivilegeWillExpire", (channelName) => {
    const channelName = channelName;            // Which Channel Token Will Expire
});

删除事件监听

为避免内存泄漏、错误和异常（即空指针异常）引起的性能下降，声网建议你在不需要使用某个事件处理程序时对其进行注销。如需注销事件监听程序，则需在添加事件监听时避免采用匿名函数的方式，以下是添加和注销事件监听程序的示例代码。

JavaScript

const messageReceived = (event) => {
    const channelType = event.channelType;      // Which channel type it is, Should be "STREAM", "MESSAGE" or "USER".
    const channelName = event.channelName;      // Which channel does this message come from
    const topic = event.topicName;              // Which Topic does this message come from, it is valid when the channelType is "STREAM".
    const messageType = event.messageType;      // Which message type it is, Should be "STRING" or "BINARY" .
    const customType = event.customType;        // User defined type
    const publisher = event.publisher;          // Message publisher
    const message = event.message;              // Message payload
    const timestamp = event.timestamp;          // Event timestamp
    // Your business processing logic program
};
// Add Event Listener
rtm.addEventListener("message", messageReceived);
// Remove Event Listener
rtm.removeEventListener("message", messageReceived);

事件通知类型

RTM 一共有 7 种类型事件，对应的有 7 种事件监听程序。你可以查看 API 参考的事件监听章节，了解每个事件监听程序传入参数的详细信息。

事件监听程序	描述
message	接收所有订阅的 Message Channel 中的消息通知或你加入的所有 Stream Channel 中订阅的 Topic 消息通知。事件负载数据中包含频道名称、频道类型、Topic 名称、事件发送者、消息负载数据类型等信息。
presence	接收所有订阅的 Message Channel 或者你加入的所有 Stream Channel 中远端用户的在线状态事件通知。事件负载数据中包含频道名称、频道类型、事件类型、事件发送者、用户临时状态数据等信息。
topic	接收加入的所有 Stream Channel 中 Topic 变更事件通知。事件负载数据中包含频道名称、事件类型、Topic 名称、事件发送者（即 Topic 详情）等信息。
storage	接收订阅的 Message Channel 及加入的 Stream Channel 中所有的 Channel Metadata 事件通知，以及所有订阅用户的 User Metadata 事件通知。事件负载数据中包含频道名称、频道类型、事件类型（即具体 Metadata 数据）等信息。
lock	接收订阅的 Message Channel 及加入的 Stream Channel 中所有的 Lock 事件通知。事件负载数据中包含有频道名称、频道类型、事件类型、锁详情等信息。
linkState	接收客户端网络连接状态变更的事件通知，包含变更前后的连接状态、服务类型、导致变更的操作类型、变更原因、频道列表等信息。
tokenPrivilegeWillExpire	接收客户端 Token 将要过期的事件通知。

完成事件监听处理程序后，你可以通过订阅频道或 Topic 来接收指定的 Message Channel 或 Stream Channel 中的消息和事件通知了。详见订阅 Message Channel 和订阅 Topic。