SelectParse Publish & Subscribe API Reference for Realtime Apps

The publish() function is used to send a message to all subscribers of a channel. To publish a message you must first specify a valid publish_key at initialization. A successfully published message is replicated across the PubNub Real-Time Network and sent simultaneously to all subscribed clients on a channel.

Messages in transit can be secured from potential eavesdroppers with SSL/TLS by setting ssl to true during initialization.

Publish Anytime

It is not required to be subscribed to a channel in order to publish to that channel.

Message Data:

The message argument can contain any JSON serializable data, including: Objects, Arrays, Ints and Strings. data should not contain special Parse classes or functions as these will not serialize. String content can include any single-byte or multi-byte UTF-8 character.

 
Do Not Use JSON.stringify!
It is important to note that you should not use JSON.stringify() when sending signals/messages via PUBNUB. Why? Because the serialization is done for you automatically. Instead just pass the full object as the message payload. PubNub takes care of everything for you.
Message Size:

The maximum number of characters per message is 32 KiB by default. The maximum message size is based on the final escaped character count, including the channel name. An ideal message size is under 1800 bytes which allows a message to be compressed and sent using single IP datagram (1.5 KiB) providing optimal network performance.

If the message you publish exceeds the configured size, you will receive the following message:

Message Too Large Error
["PUBLISHED",[0,"Message Too Large","13524237335750949"]]

For further details please check: https://support.pubnub.com/support/solutions/articles/14000113049-calculating-message-payload-size-before-publish.

Message Publish Rate:

Messages can be published as fast as bandwidth conditions will allow. There is a soft limit based on max throughput since messages will be discarded if the subscriber cannot keep pace with the publisher.

For example, if 200 messages are published simultaneously before a subscriber has had a chance to receive any messages, the subscriber may not receive the first 100 messages because the message queue has a limit of only 100 messages stored in memory.

Publishing to Multiple Channels:

It is not possible to publish a message to multiple channels simultaneously. The message must be published to one channel at a time.

Publishing Messages Reliably:

There are some best practices to ensure messages are delivered when publishing to a channel:

  • Publish to any given channel in a serial manner (i.e. not concurrently).
  • Check that the return code is success (e.g. [1,"Sent","136074940..."])
  • Publish the next message only after receiving a success return code.
  • If a failure code is returned ([0,"blah","<timetoken>"]), retry the publish.
  • Avoid exceeding the in-memory queue's capacity of 100 messages. An overflow situation (aka missed messages) can occur if slow subscribers fail to keep up with the publish pace in a given period of time.
  • Throttle publish bursts in accordance with your app's latency needs e.g. Publish no faster than 5 msgs per second to any one channel.
To Publish a message you can use the following method(s) in the Parse SDK:
  1. ParameterTypeRequiredDescription
    callbackFunctionOptional for sync, Required for asyncExecutes on a successful publish.
    channelStringYesSpecifies channel name to publish messages to.
    messageJSONYesThe message may be any valid JSON type including objects, arrays, strings, and numbers.
    publish_keyStringOptionalSpecifies the required publish_key to use to send messages to a channel.
    store_in_historyBooleanOptionalIf true the messages are stored in history, default true.
    errorFunctionOptionalExecutes on a publish error.

Publish a message to a channel:

pubnub.publish({
	channel : 'my_channel',
	message : 'Hello from the PubNub Javascript SDK!',
	callback : function(m){
		console.log(m)
	}
});
 
Before running the above publish example, either using the Debug Console, or in a separate script running in a separate terminal window, subscribe to the same channel that is being published to.
The function returns the following formatted response:
[1, "Sent", "13769558699541401"]
  1. pubnub.publish({
    	channel  : 'my_channel',
    	message  : { 
    		"a"  : 1 
    	},
    	callback : function(m){
    		console.log(m)
    	}
    });
The fire endpoint allows the client to send a message to PubNub Functions Event Handlers. These messages will go directly to any Event Handlers registered on the channel that you fire to and will trigger their execution. The content of the fired request will be available for processing within the Event Handler. The message sent via fire() is not replicated, and so will not be received by any subscribers to the channel. The message is also not stored in history.
To Fire a message you can use the following method(s) in the Parse SDK:
  1. ParameterTypeRequiredDescription
    callbackFunctionOptional for sync, Required for asyncExecutes on a successful publish.
    channel StringYesSpecifies channel name to publish messages to.
    message JSONYesThe message may be any valid JSON type including objects, arrays, strings, and numbers.
    publish_keyStringOptionalSpecifies the required publish_key to use to send messages to a channel.
    error FunctionOptionalExecutes on a publish error.

Fire a message to a channel:

pubnub.fire({
    channel : 'my_channel',
    message : 'Hello from the PubNub Javascript SDK!',
    callback : function(m){
        console.log(m)
    }
});