Node.js v14.19.3 documentation

Public API#

Overview#

Following is a simple overview of the public API.

const diagnostics_channel = require('diagnostics_channel');

// Get a reusable channel object
const channel = diagnostics_channel.channel('my-channel');

// Subscribe to the channel
channel.subscribe((message, name) => {
  // Received data
});

// Check if the channel has an active subscriber
if (channel.hasSubscribers) {
  // Publish data to the channel
  channel.publish({
    some: 'data'
  });
}

diagnostics_channel.hasSubscribers(name)#

• name <string> | <symbol> The channel name
• Returns: <boolean> If there are active subscribers

Check if there are active subscribers to the named channel. This is helpful if the message you want to send might be expensive to prepare.

This API is optional but helpful when trying to publish messages from very performance-sensitive code.

const diagnostics_channel = require('diagnostics_channel');

if (diagnostics_channel.hasSubscribers('my-channel')) {
  // There are subscribers, prepare and publish message
}

diagnostics_channel.channel(name)#

• name <string> | <symbol> The channel name
• Returns: <Channel> The named channel object

This is the primary entry-point for anyone wanting to interact with a named channel. It produces a channel object which is optimized to reduce overhead at publish time as much as possible.

const diagnostics_channel = require('diagnostics_channel');

const channel = diagnostics_channel.channel('my-channel');

Class: Channel#

The class Channel represents an individual named channel within the data pipeline. It is use to track subscribers and to publish messages when there are subscribers present. It exists as a separate object to avoid channel lookups at publish time, enabling very fast publish speeds and allowing for heavy use while incurring very minimal cost. Channels are created with diagnostics_channel.channel(name), constructing a channel directly with new Channel(name) is not supported.

channel.hasSubscribers#

• Returns: <boolean> If there are active subscribers

Check if there are active subscribers to this channel. This is helpful if the message you want to send might be expensive to prepare.

This API is optional but helpful when trying to publish messages from very performance-sensitive code.

const diagnostics_channel = require('diagnostics_channel');

const channel = diagnostics_channel.channel('my-channel');

if (channel.hasSubscribers) {
  // There are subscribers, prepare and publish message
}

channel.publish(message)#

• message <any> The message to send to the channel subscribers

Publish a message to any subscribers to the channel. This will trigger message handlers synchronously so they will execute within the same context.

const diagnostics_channel = require('diagnostics_channel');

const channel = diagnostics_channel.channel('my-channel');

channel.publish({
  some: 'message'
});

channel.subscribe(onMessage)#

• onMessage <Function> The handler to receive channel messages
  • message <any> The message data
  • name <string> | <symbol> The name of the channel

Register a message handler to subscribe to this channel. This message handler will be run synchronously whenever a message is published to the channel. Any errors thrown in the message handler will trigger an 'uncaughtException'.

const diagnostics_channel = require('diagnostics_channel');

const channel = diagnostics_channel.channel('my-channel');

channel.subscribe((message, name) => {
  // Received data
});

channel.unsubscribe(onMessage)#

• onMessage <Function> The previous subscribed handler to remove
• Returns: <boolean> true if the handler was found, false otherwise.

Remove a message handler previously registered to this channel with channel.subscribe(onMessage).

const diagnostics_channel = require('diagnostics_channel');

const channel = diagnostics_channel.channel('my-channel');

function onMessage(message, name) {
  // Received data
}

channel.subscribe(onMessage);

channel.unsubscribe(onMessage);